To better determine the range of normal values of hypoxic and hypercapni ventilatroy drives in man, these drives were measured in 40 males and 4 females between 21 and 51 yr of age. The average hypoxic drive, expressed as parameter A, was 186 plus or minus 12.8 (SEM). The average hypercapnic drive, expressed as the slope S, was 2.69 plus or minus 0.19. The range of values for these individuals was large and could not be accounted for by variations in maximal oxygen uptake, age, or sex. However, positive correlations were found between these drives and height and weight, and a positive correlation was found between hypoxic and hypercapnic drive.