We have cultured human Wilms' tumors (nephroblastomas) in vitro and examined their growth properties, tumorigenicity in nude mice, karyotypes, and production of a platelet-derived growth factor (PDGF)-like activity (PDGFc). The cultured Wilms' tumor cells do not exhibit transformed growth properties, senesce after 15-25 passages, and are not tumorigenic in nude mice. Two of the three Wilms' tumors examined had karyotypic abnormalities but none contained a deleted 11p region. The Wilms' tumor cells and control human fetal kidney cells produce significant amounts of PDGFc and express few PDGF receptors on the cell surface. Analysis of Wilms' tumor cell RNA using probes specific for PDGF A-chain and B-chain (c-sis) detects A-chain but not B-chain transcripts in the tumor cells.