The effects of different weekly exercise exposures on retention of cardiovascular fitness was studied in 21 subjects who were first conditioned by 5 weeks of bicycle ergometer exercise with work rates set to accelerate the heart rate to 80% of its maximum. They were then divided into four groups which exercised one, two, three or four times per week at the same work rate (i.e., heart rate 80% maximum) for five more weeks. Subjects were tested before conditioning (test I), after conditioning (test II), and after exercising at different weekly exposures (test III), for maximum V̇O2, maximum V̇E, maximum HR, 5-minute recovery HR, O2 pulse, V̇EO2, MVV80, FVC, FEV1.0, FEV1.0%FVC, hemoglobin, hematocrit, postexercise blood pressure, and weight. Correlated t tests of differences between tests I and II showed improvement in maximum V̇O2, maximum V̇E, 5-minute recovery HR, O2 pulse, FEV1.0%FVC and a higher hematocrit. Significant F-ratios (covariance analysis) were found among groups on test III for maximum V̇O2, recovery HR and O2 pulse. Employing these three measures in a discriminatory analysis indicated that cardiovascular fitness was retained by exercising three times per week. Pulmonary function improvements were apparently easier to retain than those of cardiovascular function.