The surface-enhanced Raman scattering (SERS) spectra of polydrin of Trabala vishnou nuclear polyhedrosis virus (sample 1) and polydrin of Dendrolimus punctatus nuclear polyhedrosis virus (sample 2) adsorbed in silver hydrosol were investigated. The features in the adsorption mode, enhancement character and mechanism of the SERS spectra of these two samples were compared and are discussed. It was found that the molecules of sample 1 adsorbed on the silver surface through carboxyl and amino groups, and the molecules of sample 2 through the sulfur atom and also carboxyl and amino groups. The chemisorption of the molecules of both samples and their short-range character indicate that the molecular mechanism is the primary enhancement in the SERS spectra of molecules of these two insect viruses. Copyright © 2001 John Wiley & Sons, Ltd.