Cultured apple cells (Malus domestica) were heat-treated at temperatures from 24 to 42 °C and measurements carried out of cell viability and gene expression immediately after heat treatment. The effects on gene expression of temperature, heat treatment duration, and recovery at 25 °C after heat treatment were also studied. An increase in expression of heat shock protein (hsp) mRNA transcripts was detected within 5 °C of the culture growth temperature. Maximum levels of expression, which were maintained for at least 3h on return to 25°C after heat treatment, occurred for heat treatments at 38°C. Cell viability was positively correlated with the expression of hsps.