Ninety-three collections of leucocytes by cytapheresis followed by separation of monocytes by centrifugal elutriation were undertaken in twelve metastatic cancer patients (four melanomas, six colon carcinomas, one ovarian carcinoma, and one lung cancer). The leucaphereses were performed aiming to collect a product, ready for introduction into the elutriation chamber, i.e., with low contamination by erythrocytes and granulocytes. The median collection of leucocytes was 7.3 x 10(9). After elutriation, purified monocytes (mean: 0.91 x 10(9)) were cultured with 3-5% autologous serum for 7 days in the presence of 250 IU/ml of recombinant human gamma-interferon (Rh-IFN gamma) for the last 18 h of culture. The median number of activated macrophages (MAK) available for reinfusion was 2.4 x 10(8) for each culture. The phenotypes and the antitumoral potentiality of MAK cells were documented. Reinfusions performed i.v. or i.p. were well tolerated with no major side effects. No complete tumor response was obtained. One partial response and two stabilizations of the disease were observed in one melanoma and two colon carcinomas.