In 30 males of a mean age 45.6 years suspected of asbestosis the author compared maximal oxygen consumption symptom limited, ventilation during consumption of oxygen (1 L per min) VE1.0 pulse rate on this level (HR1.0) and respiratory volume during ventilation 30 L X min.-1 (VT30) registered during exercise tests with an increasing load of 30 W every 3 minutes (group A) and 15 W every 1 minute (group B). Although both tests were judged to be equally stsrenuous the B test was shorter by one third and produced significantly higher VO2SL 1.89 L X min.-1, A: 1.71 L X min.-1 (p 0.01). Important diagnostical tests evaluating respiratory VE1.0, VT30 and circulatory (HR30) cost did not differ between groups. The author corroborated earlier studies that VE1.0 is one of the most sensitive tests of unequal ventilation and/or diffusion disorders in patients with slightly abnormal respiratory parameters: VC = 83% pred. FEV = 84% pred., FEV1% = 71%, DLCO = 82% pred. The results of this study show that test B is better than test A, being mich better tolerated.