Human decidua in the third trimester of pregnancy contains at least four different cell types (stromal cells, macrophages, T-lymphocytes and granulocytes). The contributions of these cells to the overall function of the tissue are not known, although it is anticipated that both stromal cells and macrophages will produce the prostaglandins involved in labour. In addition, the decidua produces cytokines, but the cellular source has not been identified. As a first stage to addressing these questions, we have developed magnetic separation methods to obtain enriched populations of decidual macrophages which contain at least 5 x 10(6) cells. We found that a preparation of up to 10(7) cells which are up to 80% pure (as assessed by a fluorescence-activated cell sorting procedure) and approximately 90% pure (as assessed by immunocytochemistry) can be obtained reliably with this method. These cells are viable for at least 48 h in culture after the enrichment procedure, and produce prostaglandins after stimulation with interleukin-1 beta.