In this study physical work capacity, mechanical efficiency on the bicycle ergometer and daily physical activities were compared between 24 physically handicapped and 24 non-handicapped children. As a measure of mechanical efficiency and physical work capacity, the oxygen uptake per kg body weight at 0.5 watt . kg-1 and oxygen uptake per kg body weight at a heart rate of 150 beats . min-1 were used. The daily physical activities were recorded during a 24-h period by means of a scoring list. The load imposed by the daily physical activities was investigated by registration of heart rate. The mean value of the physical work capacity of the group of handicapped children was found to be lower compared with the non-handicapped children. The mechanical efficiency of 7 of the 24 handicapped children was lower when compared with the mechanical efficiency of 23 of the 24 non-handicapped children. A significant correlation between mechanical efficiency and nature of the handicap (spastic hemi-, di-, tetraplegic) was found (p less than 0.05). During light daily physical activities the handicapped children showed the same mean heart rate as the non-handicapped children, but the mean heart rate during heavy daily physical activities was lower for the handicapped group than for the non-handicapped group. The non-handicapped children spent more time in physical activities with relatively high heart rates. From the results obtained of oxygen uptake and heart rate measurements it is to be expected that non-handicapped children are able to maintain a higher state of training by means of their daily physical activities than are handicapped children.