A steady state diffusing capacity (DLCO) has been measured in 509 healthy (normal) adults (288 males and 221 females) of the age between 18 and 74 years. Obtained DLCO values were related to age, height, body weight and body surface area. Data suggest that there is a good correlation between observed independent variables and DLCO, although there were differences related to sex, presumably because of wide individual variation. Regression equations for predicted values of DLCO were derived. The regression equation based on age in nonsmokers is: Men: DLCO: 28.5705--0.1428 x years + 0.0104 x height in cm; Women: DLCO: 7.4519--0.0406 x years + 0.1910 x height in cm. The predicted values of DLCO, regardless to smoking, are presented in table form, which can be used in everyday work.