Throughout the winter of 1984-1985, daily hive and cluster temperatures were recorded in a group of 4 insulated, outdoor wintering (Apis mellifera L.) colonies at 8.00 h.min and again when bee activity and bee-induced entrance defrosting was observed. The latter process was observed on 4 separate occasions during the winter following prolonged cold periods. It occurred in the afternoon of the 1st and 2nd days with the increased temperatures. During the process, the cluster 30°C isotherm extended to the hive top entrance whether it faced N or S, the entrance temperature increased to 35°C, the frost melted, and the bees appeared at the top entrance. Some worker bees rushed out into the snow while many others walked or clustered outside the entrance. This behaviour occurred at ambient temperatures as low as -8·8°C. Only slight temperature changes were observed in other parts of the hive and cluster.