We examined the production of parathyroid hormone-like protein (PLP) by all major lung cancer cell types, including epidermoid, small cell, and adenocarcinoma. We demonstrated that cell lines derived from each cell type released PLP into culture medium. To determine the predominant species of PLP produced by the cell lines, guanidine hydrochloride extracts were prepared and analyzed for PLP by high performance size exclusion chromatography under denaturing conditions. Cell lines from each of the major lung tumors produced multiple and different forms of PLP. The estimated molecular sizes of the PLP species ranged from 3.5–11.7 kilodaltons. Our results demonstrate that PLP is produced by all major lung cancer cell types and extend these observations to adenocarcinoma and large cell carcinomas of the lung. Furthermore, we observed PLP heterogeneity among these different cell types, which may represent tissue-specific PLP processing among different human lung tumors. (Endocrinology129: 2466–2470, 1991)