The computer program SEECAL, written by Cristy and Eckerman from the Oak Ridge National Laboratory, USA, calculates specific effective energies (also known as S factors in the MIRD terminology) for an adult male, an adult female and five paediatric ages. Its dosimetric methodology is that of the ICRP. Among other parameters, SEECAL requires input data on specific absorbed fractions (SAF) and utilises those derived from the MIRD-type stylised anthropomorphic phantoms. SEECAL has been used worldwide for dose estimations concerning occupational or public exposures due to radionuclides incorporated into the body and has formed the basis for programs developed by other laboratories to calculate, for example, dose to the patients undergoing nuclear medicine procedures. The revised version of SEECAL is at the moment limited to adults and utilises the photon SAFs derived with Monte Carlo methods for the new reference male and female voxel-based phantoms to be adopted by the ICRP.