We have demonstrated that restriction endonuclease (REN) analysis of the DNA genomes of baculoviruses used as biological pesticides provides a rapid and precise method for the identification of the viruses. We have recommended that this identification method be employed for quality control of commercial virus preparations as well as pre-registration characterization of viral persticides. The REN analyses have also provided information on the sequence homology of several viruses previously considered to be different viruses. Our results indicate that A. californica MNPV, T. ni MNPV and R. ou MNPV are genotypic variants of a single virus. We have also developed a method for cloning a multiple-embedded nuclear polyhedrosis virus (an MNPV). In the course of this work, we discovered five distinct genotypic variants of A. californica MNPV. We have recommended that cloning of viruses be a prerequisite for pesticide registration. The implementaton of our results in viral pesticide registration procedures and quality control of commercial virus preparations is expected to increase the safety margin of using viruses as insect pest control agents.