Sixteen patients with disseminated melanoma were immunised with either BCG (8 cases) or C. parvum (8 cases) on three occasions at 21 day intervals. Blood for assay was taken immediately before the first immunisation and weekly for eight weeks thereafter. Total white count tended to increase but little change was seen in lymphocyte and monocyte counts. Serum IgG increased after BCG BUT NOT WITH C. parvum, serum IgA and IgM did not alter. The 'E' rosette % did show some increase mainly after C. parvum, and 'B' lymphoid cells (sIg staining) increased slightly after BCG; the 'EA' rosette % fell following C. parvum but not after BCG. Lymphocyte PHA blastogenesis increased after immunisation, particularly with BCG. Non-specific lymphocytotoxicity (51 Cr Chang target) demonstrated dramatic increases for 'non T' and 'K' cell function and a smaller increase in 'T' cell cytotoxicity following immunisation. These increases in cytotoxicity were maintained by the 21 day immunisation schedule.