AIM--To examine lymphocyte subsets in patients with myelodysplastic syndromes (MDS); and to correlate immunohistological variables with prognosis. METHODS--Bone marrow trephine biopsy specimens from 65 patients with MDS were immunophenotyped using a panel of antibodies. A minimum of 1000 cells from representative areas of marrow sections were counted at light microscopy. The association between immunohistological variables and prognosis was assessed. RESULTS--Compared with normal control marrows (n = 23) no major abnormalities of T cells (CD3), T cell subsets (CD4, CD8, CD25, TCR gamma/delta) or natural killer cells (CD56, CD57) were seen in the 65 patients. In high risk MDS (RAEB, RAEB-t) 19% of the cases showed increased numbers of B lymphocytes compared with none in the low risk group (RA, RARS) (p < 0.0090). Only percentages of B cells above 3% significantly correlated with poor survival (p = 0.0121 for CD19, p = 0.046 for CD22). CONCLUSIONS--The deviations in T lymphocyte counts seen in peripheral blood and in bone marrow aspirates could not be verified in bone marrow biopsy specimens.