General Comments: A report is prepared about the radiation induced cancer risk at low dose extrapolation with the possible implications for radiation protection. As a result, it is recommended that radiation protection continues to be guided by the linear, no-threshold (LNT) model. The document is a very helpful review about the results of molecular radiation biology (literature review until beginning 2004). The radiation biology review takes about five times more pages as compared to the epidemiological part. The question can be asked if it should be the task of ICRP to produce such a comprehensive review of the scientific radiation biology literature which will be outdated in short time. There is much speculation presented about the implications of genomic instability, adaptive response, bystander effect etc.. However, an ICRP document is considered to presented the „hard“ facts or the evidence without doubt that are used for radiation protection recommendations. Specific comments: Chapter 1: Introduction Some recent reviews about the low-dose radiation effect relationship should be mentioned besides NCRP- and UNSCEAR-reports, like: Advisory Committee on Radiological Protection, 1996. Biological Effects of Low Doses of Radiation at Low Dose Rate. ACRP-18. Ottawa, Canada, AECB. Tubiana, M.,2003. The carcinogenic effect of low doses: the validity of the linear no-threshold relationship. Int. J. of Low Radiation, 1: 1 – 33. The definition of low dose changes several times: Is 10 mSv low, 100 mSv moderate as indicated at page 13, line 7-9 , or low doses on the order of 100 mGy (page 13, line 34) or less 500 mGy (page 146, line 17) ? Low Dose stated as Gy or Sv ? There should be an explanation, why the sequence of the report is epidemiology – radiation biology – uncertainties. Why not start with initial radiation damage, radiation biology, animal experiments, epidemiolgy like UNSCEAR. Chapter 2: Epidemiological Considerations The dependence of cancer risk on radiation dose is not explained in section 2.2 (title of pages 22 – 23). It is not obvious why these data about exposure levels are given here (page 23, line 8 – 20), similar data are found on page 31/32. Page 40, line 8: Citation Brenner and Raabe, 2001, why not an ICRP citation ? Chapter 3: Low Dose- Biology This part is well written and treated in great detail. New results are reviewed in the fields of DNA repair and cell cycle control. It is argued against the likely possibility of a threshold for radiation induced cellular effects. The written text without any graphics makes it difficult to understand some details. Page 60, line 20-21: Render this proposition untenable – to strong Page 63, line 12: Two coiled coil tails ? Chapter 4: Cellular Consequences of Radiation-Induced Damage Transgenerational instability is not treated thoroughly. Some investigations about radiation induced genomic instability in connection with the atomic bomb cohort and the Chernobyl accident (clean-up workers, population) are missing, e.g. Livshits, LA et al.,2001, Radiat. Res. 155:78-80; Dubrova, Y.E. et al.,2002, Am.J.Hum.Genet. 71: 801-809; Kiuru, A. et al., 2003, Radiat. Res. 159: 651-655; Furitsu, K. et al., 2005; Mutat. Res. 581:69-82; Kodaira, M.1995, Am. J. Hum.Genet. 57: 1275-1283. Page 115, line 5: Citation is missing Chapter 5: Carcinogenic Effects of Ionizing Radiation This is the only chapter with underlined sentences. The reason for underlining is not always obvious. There are several hypothesis discussed. In connection with radiation induced cancer in animals (section 5.3, page 146) it is anticipated, it appears, it does not appear, can be predicted etc. Here, more conclusions are needed. It is stated that the derivation and application of dose and dose rate effectiveness factors (DDREF) must be performed with caution (page 153, line 28/29).. How is caution applied ? The application of DDREF is problematic (page 154, line 28). Data about the low-dose radiation activation of the immune system are missing (e.g., Ina et al., 2005, Rad. Res. 163: 153 – 158). Chapter 6: Quantitative Uncertainty Analysis In addition, the precautionary principle might be discussed in this chapter. Chapter 7: Conclusions Page 189, line 20: misprint on the whole. Page 189, line 28: why not 60 mGy (see page 36) Page 190, line 21-23: It is speculated that the ionising radiation induced type of damage may not be generated by endogenously or exogenous agents, and may not have been a strong selective pressure driving efficient repair. A speculation should not be part of the conclusions.