Metacyclogenesis of Leishmania major in an acidic medium.

An acidic medium was used to stimulate the production of a homogeneous stationary phase promastigotes, morphologically and functionally similar to the in vivo infective form. They possessed a short (< 8 Um) and narrow (< 1.5 Um.) cell body with a flagellum twice or more its length. They were PNA, highly infective to peritoneal macrophages in vitro and expressed high phosphatase activity. By elevating the incubating temperature, almost all of these promastigotes were transformed to amastigotes.