ABSTRACT.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 &OV0312;O2, maximum &OV0312;E, maximum HR, 5‐minute recovery HR, O2pulse, &OV0312;EO2, MVV80, FVC, FEV1.0, FEV1.0%FVC, hemoglobin, hematocrit, postexercise blood pressure, and weight. Correlatedttests of differences between tests I and II showed improvement in maximum &OV0312;O2, maximum &OV0312;E, 5‐minute recovery HR, O2pulse, FEV1.0%FVC and a higher hematocrit. Significant F‐ratios (covariance analysis) were found among groups on test III for maximum &OV0312;O2, recovery HR and O2pulse. 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.