Norms for hand grip strength of healthy children are presented. Sex and age specific centiles for age 5 to 18 years have been determined using a portable strain gauge dynamometer with an accuracy of 0.5 N. The test group comprised 1417 healthy, urban school children from a middle class suburb of Brisbane. Mean maximum grip strength (of four tests, two with each hand) and mean peak grip strength (best of four tests) were recorded. Mean values of peak grip strength were 10 to 15% higher than the average maximum grip in all age groups. At all ages girls had a reduced grip strength compared with boys and although boys manifested a continual, approximately linear increase in grip strength through all age groups, girls manifested an approximately linear increase up to 13 years after which mean hand grip usually remained constant. By the age of 18 years boys had a mean grip strength some 60% higher than girls. Correlations with height and weight are also presented. "Handedness' influenced grip strength and was most noticeable in children aged over 10 years. The clinical use of hand grip strength centiles for the early indication of neurological and muscular disorders and for following the natural history of neuromuscular disease is discussed.