In the course of a study on the health effects of vermiculite, 653 black rural industrial workers had their lung function measured. Since the study revealed no health effects of their industrial environment, the group was used to determine prediction equations for black men. Vital capacity, forced vital capacity, forced expiratory volume in 1 second, and peak flow were appreciably higher than the predicted values for blacks in the USA. The predicted values were, however, lower than those reported for white non-smokers but significantly higher than those reported for a non-smoking group of black miners in South West Africa/Namibia.