Macrophages have been isolated from ascitic and collagenase-dispersed tumours from patients undergoing surgery for ovarian cancer. Macrophages were present in varying proportions in both sites, though the ration of macrophages to tumour cells was higher in ascites. Marked variation in size (as detected by sedimentation velocity) and cytochemical markers in the macrophages was noted. Highly enriched macrophage fractions were isolated from the ascites and collagenase-dispersed solid tumours by a combination of sedimentation velocity and selective EA RFC or adherence techniques. Suppressor activity in the PHA assay was detected in tumour macrophages (4/10 giving less than 50% inhibition), ascitic macrophages (1/15) and blood monocytes (2/7). Lymphocyte fractions from tumours were unresponsive to PHA and failed to suppress the blood response. Suppressor activity was also present in the purified tumour-cell fraction of 6/14 patients. ADCC activity was tested in a few patients. When the activity was determined against the SB target cells, tumour-derived macrophages were inactive, whereas the ascitic fraction showed low but significant activity which averaged much lower than patients blood values. The ADCC assays carried out with the CRC target cell indicated activity within the range of patient blood values in 4/4 ascites and 2/4 tumour macrophage fractions. Cytotoxicity was also assessed against co-purified autologous tumour cells. Although activity was detected in many of the tests, the results seemed to reflect target cell sensitivity. There appeared to be a correlation between cytotoxicity with test macrophages and normal blood mononuclear cells. The results indicate that the cytochemical heterogeneity and the variation in size between macrophage fractions is associated with a spectrum of activities.