A panel of 10 monoclonal antibodies reactive with formalin-resistant epitopes was applied to characterize the giant cells of the Reed-Sternberg, Hodgkin, and lacunar cell types in diagnostic biopsies from the German Hodgkin Trial. The 94 tissue samples examined had been sent to the Reference Center by 44 different laboratories which made the initial diagnoses. A board of four referees re-classified the primary diagnoses established by the 44 different histopathologists, providing subtyping of Nodular Sclerosis according to Bennett et al. (1985, 1989). Only cases with unequivocal agreement among the referees and which satisfied standards of fixation and embedding were included. Giant cells stained positively with: Ber-H2 in 92 per cent (81/88), LN-2 in 86.4 per cent (76/88), and DAKO-M1 in 72.2 per cent (64/88) of cases in which the lymphocyte predominance type was not included. Positive staining was quite rare with the other seven monoclonal antibodies. No significant difference in reactivity was revealed between giant cells of Reed-Sternberg, lacunar or Hodgkin cell types. Approximately one third of the cases were negative for at least one of the markers, Ber-H2, LN-2 or DAKO-M1. The lymphocytic and histiocytic cells in lymphocyte predominance Hodgkin's disease displayed a distinctive staining pattern with positivity for B-cell markers, whereas DAKO-M1 and Ber-H2 were predominantly negative. Finally, we found that randomly collected blocks of primary biopsies permit reliable immunostaining by this panel of monoclonal antibodies, since our results agree with results from the literature obtained from biopsies processed according to more uniform protocols for fixation and embedding.