Values of HE/D, the ratio of the effective dose equivalent HE to the mean absorbed dose D to the total body, have been derived as a function of beam quality (HVT) for a variety of Roentgen diagnostic examinations of the adult trunk and head, using tabulations from the literature. Problems in specifying beam quality are discussed. The energy epsilon imparted to the patient can, in Roentgen diagnostic examinations, be determined using a transmission chamber. Since, however, HB/epsilon depends more critically than HE/D on the mass M of the patient (D = epsilon/M), the latter quantity is preferred for risk assessment. HE/D takes values in the range 0.44-2.8 Sv Gy-1. This includes the value 1 Sv Gy-1 resulting from a uniform whole-body irradiation independent of M. The corresponding value of HE/epsilon = 1/M Sv J-1 if M is in kg. It is therefore recommended that clinical measurements of epsilon be supplemented by measurements of the patient's mass so that D = epsilon/M can be estimated and tabulations of organ absorbed doses be supplemented with values of D so as to allow accurate derivation of the ratio HE/D. In optimising the technical parameters of a given examination using the transmission chamber, HE/D as a function of beam quality must be known.