The aim of this study was to estimate the resistance of the viral genome of coxsackie B3 to heat (from 25 degrees C to 95 degrees C) with respect to the infectious virus. The results show that viral genomes were much more resistant to heat than infectious virus. The infectious coxsackie B3 was undetectable following incubation at 55 degrees C for 15 min., while the viral genome was still detected after incubation at 95 degrees C for 15 min. The viral genome became undetectable by RT semi-nested PCR after incubation at 95 degrees C for 30 min. We suggest that the rapid loss of infectious ability of the virus after incubation at 55 degrees C may be mostly due to cleavage or conformation changes in the viral capsid without significant destruction of the genome.