Simple, valid, and reliable methods of estimating maximal oxygen uptake (&OV0312;O2max) are needed for epidemiologic studies of physical activity, to evaluate fitness for job performance, and to assist in prescription of exercise. Such estimations in women have not received due research attention. Heart rate responses to submaximal cycle ergometry and &OV0312;O2maxduring maximal treadmill and cycle ergometer testing were measured in 37 healthy women aged 19–47 yr (X = 31.7 ± 7.9). The submaximal test was very reliable on retest (r = 0.92), but overestimated measured treadmill &OV0312;O2max(&OV0398; = 2.42 vs 2.23 1·min−1; r = 0.76, SEE = 0.229). The submaximal test also greatly overestimated maximal cycle ergometer &OV0312;O2max(&OV0398; = 2.42 vs 2.06 1·min−1; r = 0.70, SEE = 0.340). Similar 8.5% (treadmill) and 18.5% (cycle ergometer) overestimations by the submaximal test were found for &OV0312;O2maxrelative to body weight. A simple submaximal exercise test is highly reliable as an estimate of &OV0312;O2maxwhen used for women. It also provides a reasonably good estimate of treadmill measured &OV0312;O2max.