A measles-virus-carrier cell line, designated AV3/MV, was derived from established human amnion (AV3) cells surviving primary infection with the Edmonston strain of measles virus. During maintenance of infected cultures in the laboratory, the cells passed from a highly productive chronic phase (where infectious virus was continuously shed) to a less productive degenerative phase (where fewer infectious particles were produced). Carrier cultures in the less-productive phase gradually deteriorated and failed to survive at 37 degrees. However, when temporarily maintained and passaged at 39.5 degrees, the cultures stabilized and carried the virus in a latent or nonproductive state. Carrier cultures in the chronic phase of infection expressed variable degrees of virus-specific CPE, replicated erratically, and generated large amounts of virus-specific antigens. In the stabilized latent phase, the cultures demonstrated no virus-specific CPE, replicated steadily, and generated reduced amounts of virus-specific antigens. The results of our studies indicate that the establishment and maintenance of persistent measles virus infections in AV3 cells are dynamic processes involving numerous variables, and that there are similarities between these latent-carrier cell lines and certain virus-carrier cell lines derived from subacute sclerosing panencephalitis brain tissues.