Diffusing capacity (DLCO) was measured in 260 healthy subjects aged 60-86 years who were leading an active life in the community. DLCO correlated with body surface area and spirometric indices, and declined with age. It was lower in women, in smokers and in those with chronic bronchitis. Multiple regression equations based on age and body surface area were derived for elderly Chinese men and women. Compared with predicted values based on studies of Caucasians of all ages, those for elderly Chinese men were higher, while those for elderly women were similar. Predicted values for an elderly Chinese population should be derived from equations established from this survey rather than those extrapolated from Caucasians of all ages. DLCO/VA correlated with weight and body surface area but not with height, and declined with age. There was no difference between men and women, and between those with or without symptoms of chronic bronchitis. Predicted values from this study of elderly Chinese were comparable to those derived from Caucasians of all ages. Differences in DLCO values for elderly Chinese compared to Caucasians may be explained by differences in lung volumes rather than ethnic variations in the diffusing characteristics of the alveolar capillary membrane, and by the small numbers of elderly subjects in some of the studies of Caucasian subjects.