Formalin-fixed tissue biopsies from 29 women with the histological diagnosis of severe endometritis were examined for chlamydial antigen by fluorescein-conjugated monoclonal chlamydial antibodies (SYVA) technique; 15 (52%) were positive. In nine patients also samples for isolation of Chlamydia trachomatis by cell-culture technique were obtained peroperatively; seven were culture-positive. In all these patients fluorescent chlamydial antigen was detected, whereas the two culture-negative patients had no such antigen. The technique presented makes it possible to examine series of formalin-fixed endometrical biopsies to evaluate the significance of C. trachomatis being etiologic agent in endometritis in females.