AbstractThe radiation doses given to 20 mothers and foetuses during intra-uterine transfusions for Rh-iso-immunization are assessed. Details are given of the method used for these calculations together with the technique of the procedure, as used in this hospital.It is calculated that the average mother received a skin exposure of 3,312 mR during amniography and 3,310 mR during fluoroscopy. For radiography the range was 1,450 mR (Case 8) to 5,230 (Case 14) and for fluoroscopy from 942 mR (Case 5) to 7,795 mR (Case 3). The average foetal dose was assessed at 617 mrads—varying from 247 mrads in Case 5 to 1,117 mrads in Case 3.The sources of error inherent in these calculations are given.It is concluded that the foetal radiation dose in this series is acceptable, although it is probably above 1 rad in several cases.