The graded treadmill (TM) exercise test is considered the optimal mode of exercise for evaluating the cardiovascular fitness of mentally retarded (MR) individuals. A new mode of exercise, the Schwinn Air-Dyne ergometer (SAE), was evaluated and compared to the TM for determining the cardiovascular fitness of adults. Twelve MR adults performed maximal exercise tests to volitional exhaustion, on separate days, on the SAE and TM. Maximal heart rates, oxygen consumption, minute ventilation, and respiratory quotient were similar for both exercise tests. These results indicate that the SAE is comparable to TM exercise in assessing the cardiovascular capacity of MR adults.