Anthropometric and body density measurements were made on 105 coastal and 115 highland 17-48 year old New Guinean men and women. The two groups experienced different physical, biological and social environments, the highland group being less exposed to new influences. These New Guineans were short in stature (men 1.61 SD 0.05 m, women 1.52 SD 0.05 m), light in weight (men 57.4 SD 5.0 kg, women 49.4 SD 5.4 kg), lean (men 10 SD 4% fat, women 21 SD 4% fat) and muscular compared with most European populations. Highland men had greater body weights and fat-free masses than coastal men but stature, body density, skinfold thickness and fat mass were similar in the two groups. In the women, there were significant negative correlations of age with body weight, skinfold thicknesses, fat-free mass and fat mass which contrasts with the changes seen in European populations. The correlations of body density with log sigma four skinfolds were low, probably because of the homogeneity of the groups. Body density was reliably estimated in women but not in older men from equations drawn up from samples of Europeans.