A rabbit nesting box incorporating a low wattage heated floor was developed. In a preliminary study a floor surface temperature in the box of 27°C was found to be adequate to minimize chilling of young pups in the nest. A full scale trial followed using 44 crossbred does, 22 provided with a nestbox containing a heated floor and 22 with a control plywood nesting box. The experiment continued for six successive reproductive cycles over the period April 1981 to February 1982 in an unheated rabbitry. Throughout the year significantly more pups reached weaning age when does were provided with nestboxes containing heated floors. On average, 0·15 of all pups born to does with heated floors had died by 28 days post partum, the comparable figure for unheated floors being 0·56. This reduction in mortality in heated boxes was apparent both on the day of birth and in the subsequent weeks prior to weaning. Ambient temperature and the wetness of the nest had a strong influence on the survival of pups in control boxes with high mortality rates experienced in the cold winter months (0·79 in February 1982). Most of these deaths in the control boxes were attributable to chilling and/or starvation in the nest (0·53 of diagnosed deaths overall). The running costs of the heated nestbox system are discussed.