Insulin-like growth factor 1 (IGF-1) is shown to support the long term survival of embryonic chicken central nervous system neurons cultured in a defined medium. This trophic activity for IGF-1 was discovered as the result of its presence as a contaminant in bovine serum albumin, a reagent frequently used in primary cultures of neuronal tissue. The observation that IGF-1 has cell survival activity may explain the high level of IGF-1 receptors found in embryonic brain.