The physiological basis of training responses in women, and particularly older women, is not well understood. Short-term aerobic training (STAT) was used to probe the effects of age and hormone-replacement therapy (HRT) on women's ability to rapidly change peak uptake ( V O 2max ), plasma volume and cardiac function. A total of 39 females participated in the STAT programme: 15 younger (Y; aged 19–29 years), 12 postmenopausal women undergoing HRT and 12 non-medicating postmenopausal (PM) women (aged 60–75 years). Training consisted of ten sessions of cycling over a 2-week period, which progressed in duration from 20 to 60min and in intensity from 60–75% of maximum heart rate. Plasma volume (PV; as determined by Evan's Blue dye dilution), V O 2max (cycle ergometry) and cardiac function (radionuclide ventriculography) were analysed using analysis of covariance or repeated measures ANOVA. All groups demonstrated similar increase in V O 2max (Y, 13%; PM, 17%; HRT, 13%), but without a significant change in left-ventricular ejection fraction and diastolic function or volumes during supine exercise. PV expansion was observed among the Y group (7%; P <0.05) but not the PM group (2%; P >0.05) or women undergoing HRT (1%; P >0.05). Age and hormone-replacement status did not affect the magnitude of V O 2max change. This study suggests that STAT improves V O 2max , independent of central adaptations.