Lymantria disparL. larvae infected with the gypsy moth nuclear polyhedrosis Virus were exposed toApanteles melanoscelus(Ratzeburg) females, separately and in combination. with noninfected larvae. Significant differences established among the number of parasite-host contacts and percent ovipositional attempts observed under various treatments indicated that the parasites preferred noninfected larvae, making fewer efforts to parasitize virus-infected individuals. Since the noninfected and virus-infected larvae were different in a number of ways, several factors may have contributed to the behavioral discrimination evidenced.