Baculoviruses are widely used as bioagents for controlling insect populations. Although they are successfully replicated in cell cultures, still the production in laboratory reared larvae is the cheapest way for large-scale production of viral agents. Commercial products are prepared as liquid suspensions and as dried powders. We investigated the stability of two formulations of S. exigua nuclear polyhedrosis virus (SeMNPV) stored at +4°C for over twenty years as a powder (prepared by aceton precipitation) and in a suspension. The biological activity and biochemical properties of these formulations were examinated. Viral biological activity of the suspension was 1 OOO times better than the activity of powdered virus. Aceton precipitation method caused the significant loss of virus activity. Electrophoretic analysis of proteins showed degradation of polyhedrin peptide. There was also partial DNA degradation. These changes may lead to decreased bioactivity of powdered SeMNPV virus.