Two groups, each of eight patients, with metastatic melanoma were immunized with either C. parvum or BCG at 3-weekly intervals. The serum IgG, IgA, IgM levels, E-rosettes, EA-rosetts, sIg-bearing cells, 'null cells' and lymphocyte blastogenesis at four PHA concentrations were assayed, before immunization and weekly thereafter for 8 weeks. The pre-immunization E-rosette values were significantly reduced, with a significant increase in 'null cell' values and EA-rosette percentages, when compared with healthy controls. Following C. parvum immunization, significant increases occurred in E-rosette percentages with decreases in EA-rosette and 'null cell' counts. A significant reduction in 'null cell' values also occurred with BCG. Other parameters including PHA blastogenesis did not exhibit statistically significant changes. Different methods of expressing the results (particularly of blastogenesis data) were compared, as were the similarities between the present investigation and a study of the effects of a single immunization. The relationship between the subpopulation changes and lymphocyte cytotoxicity described in an earlier article (Thatcher, Swindell & Crowther, 1979a) is discussed.