In order to gain insight into the role of macrophages in human lung carcinomas, we investigated material from 35 lung carcinomas and 5 healthy lungs with 4 different antibodies (CD68, MRP8, MRP14, 27E10) recognizing different macrophage subtypes. Infiltration with CD68-positive macrophages was highest and comparable in healthy lungs and lung carcinomas. Compared to healthy lungs, the infiltration of MRP8- and MRP14-positive macrophages was reduced in lung carcinomas while the number of 27E10-positive cells was enhanced. No difference in the infiltration of macrophages was observed between the different histological subtypes of carcinomas such as squamous carcinoma, small lung carcinoma, adenocarcinoma and bronchio-alveolar carcinoma. Furthermore, we present a highly suitable technique for the isolation and enrichment of macrophages from human lung carcinomas resulting in a 5-10 fold enrichment and a yield of e.g. 2-3 x 10(6) 27E10-positive macrophages/g tumor biopsy. Together with the recent findings that 27E10-positive macrophages are prevalent in early acute inflammation and release cytotoxic mediators and to inhibit tumor cell proliferation our findings suggest that 27E10-positive macrophages may play a role in antitumor cytotoxicity in human lung carcinomas.