To determine the suitability of murine norovirus (MNV) as a surrogate for human norovirus (HuNoV) in heat inactivation studies. MNV, hepatitis A virus (HAV) and HuNoV genogroup I and II (GI and GII) specific real-time quantitative reverse transcription (qRT)-PCR assays were used to determine the effects of heat exposure (63 and 72 degrees C) for up to 10 min in water and milk. Using culture assays, MNV and HAV showed similar reductions in infectivity over time. Both HuNoV GI and GII showed lower log reductions in qRT-PCR titre following heat exposure than either MNV or HAV. No significant protective effect of milk was observed for any virus. MNV is as suitable a surrogate for HuNoV as HAV. In heat inactivation studies at 63 and 72 degrees C, qRT-PCR results indicate that HuNoV is less susceptible to heat than either HAV or MNV and so neither virus may be an appropriate surrogate for HuNoV. Caution should be used when extrapolating surrogate virus data for HuNoV. Although not conclusive, our results suggest that HuNoV may be more resistant to heat than either HAV or MNV.