A complete developmental sequence of Leishmania mexicana has been produced in axenic culture for the first time. This was achieved by manipulation of media, pH and temperature conditions over a period of 16 days. All experiments were initiated with lesion amastigotes that were transformed to multiplicative promastigotes by culture in HOMEM, 10% foetal calf serum, pH 7.5, at 25 degrees C. Metacyclogenesis was induced by subpassage in Schneider's Drosophila medium, 20% foetal calf serum, pH 5.5, and the resulting forms transformed to axenically growing amastigotes by subpassage in the same medium and raising the temperature to 32 degrees C. Parasites from each day were characterized with respect to their general morphology using light microscopy of Giemsa-stained smears, and biochemically by analysis of total protein content, proteinases, nucleases and secretory acid phosphatase. The results demonstrated that the three main stages identified--amastigotes, multiplicative promastigotes and metacyclic promastigotes--each exhibited the expected suite of biochemical properties. Further, the changes in morphology observed as the developmental sequence proceeded from stage to stage were accompanied by appropriate changes in biochemical properties. These results provide both useful biochemical markers and a culture system in which to examine the regulation of differentiation and transformation during the Leishmania life-cycle.