Lithium fluoride (LiF) thermoluminescent dosimeters (TLD) have been employed to measure the radiation dose distribution within a phantom and the central axis dose in air. Results are presented for seven (four EMI CT1010, one EMI CT5005, one EMI CT7070 and one Siemens DR2) different machines. Organ doses for four different computed tomography (CT) investigations (head, lung, liver and pelvis) have been estimated from previously published tables and the central axis dose in air in 3 CT units. These estimated organ doses were used in turn to deduce the somatic and genetic risks for the four types of CT examination. These calculations indicate that for an 'average' male patient undergoing a CT examination corresponding to the average conditions encountered, the total somatic risks are 3.15 10(-4), 1.98 10(-4), 2.31 10(-4), and 1.38 10(-4) for head, lung, liver and pelvis scans, respectively. The corresponding figures for female patients are 3.39 10(-4), 3.95 10(-4), 2.73 10(-4), and 1.60 10(-4). The risk from head scanning is approximately 250 times that of a dental pantomograph. Somatic and genetic risks will be approximately twice as high for contrast examinations.