The kinetics of ultraviolet inactivation for two human rhinoviruses and poliovirus were compared. No major differences in the rates of ultraviolet inactivation were detectable. All viral preparations inactivated by ultraviolet irradiation induced neutralizing antibody in guinea pigs. In contrast, when guinea pigs were immunized with a heat inactivated rhinovirus preparation, little or no neutralizing antibody was elicited. Immune electron microscopy of the heated rhinovirus preparations revealed the presence of particles resembling empty capsids. These results suggest that rhinoviruses and enteroviruses are affected in a similar manner when subjected to ultraviolet or heat inactivation.