The following is a synopsis of the conclusions of the BEIR VII phase 1 study:

In the committee's judgment, information that has become available since publication of the 1990 Health Effects of Exposure to Low Levels of Ionizing Radiations (BEIR V) makes this an opportune time to proceed with BEIR VII phase 2 –a comprehensive reanalysis of health risks associated with low levels of ionizing radiations. Such a study should begin as soon as possible and is expected to take about 36 months to complete.

The committee based that judgment on the following considerations:

• Substantial new epidemiologic evidence has accumulated since the 1990 BEIR V report was published. The present committee's phase 1 report will cite 39 new epidemiologic studies that fall into this category (see Table 1). Additional studies that have a direct bearing on the subject should become available in the next 3 years, the estimated period required to complete the phase 2 study.

• Some of the new epidemiologic data are on subjects on which information had been sparse, such as cancer mortality in those exposed to whole-body irradiation in childhood.

• Studies of carcinogenesis completed since publication of the last BEIR report have focused on mechanisms and the cellular and molecular events that are involved in the neoplastic process. The understanding of molecular events involved in carcinogenesis has increased significantly. Mechanisms that might be involved in radiation carcinogenesis have been identified. Further knowledge of these mechanisms that should become available in the next 3 years might affect estimation of the radiation-response curve at low doses.

• Over the next few years, investigators will be applying two closely linked approaches using animal models of carcinogenesis. These will likely contribute to a