Excretory-secretory products (ES) of Setaria cervi, a bovine filarial parasite, were prepared by in vitro maintenance of the worms in a protein free defined medium at 37 degrees C. RPMI-1640 medium proved to be the best as the worms remained motile in it for the maximum period of time without change of medium, and approximately 12-15 mg protein per 100 adult worms could be obtained. Crossed immunoelectrophoretic analysis of ES products revealed 11-15 antigens and most of them were common to somatic antigenic preparations from both adult worms and microfilariae. The ES products were also found to contain 3-4 host proteins, including serum albumin.