An intercomparison exercise on the determination of 241Am, 244Cm and 252Cf in urine was performed. Since it was designed with regard to emergency preparedness, the detection limit for each nuclide was set to 0.1 Bq per 24-h urine sample. Most of the participating laboratories were established bioassay laboratories. However, some laboratories that routinely determine 241Am only in environmental samples were also invited in order to explore their potential for emergency bioassay analysis. Another aspect of the intercomparison was to investigate the performance of all laboratories concerning the chemical yields of the 243Am tracer in comparison with 244Cm and 252Cf. In summary, both types of laboratories showed good results. There was a negative bias for the results of 244Cm and 252Cf, which can be explained by slightly different radiochemical behaviours of americium, curium and californium and which is in agreement with results reported in the literature.