The human anthrax vaccines currently licensed contain the protective antigen (PA) of Bacillus anthracis as main antigen together with traces of some other bacillus components, e.g. lethal factor (LF). The present study aimed at monitoring the course of specific antibody titres against PA and LF by enzyme linked immunosorbent assays (ELISA), as well as the levels of toxin-neutralising antibodies, in 11 volunteers vaccinated with the human anthrax vaccine UK. After an initial seroconversion in all vaccinees, a significant reduction of both antibody titres against PA and LF, and of neutralising antibodies, was detected just prior to a vaccine boost 6 months after completion of the basic immunisation. Following the booster injection, titres increased again to levels comparable to those after the fourth immunisation. ELISA titres against PA correlated significantly with neutralising antibodies (r=0.816, p<0.001). Therefore, the less work- and time-consuming ELISA should be favoured to monitor the efficacy of an anthrax vaccination.