The present study was undertaken to determine if a model accounting for reaction time (RT) on the basis of the EEG alpha rhythm and refractory period (RP) could predict RT in young and old adult subjects. Ten male university undergraduates and ten community residing males over the age of 65 had resting EEG recorded at right and left occipital sites. Mean alpha frequency was 1.2 Hz slower in old subjects. RT and RP were assessed in a warned RT paradigm. Sixty-four trials of each of a 50, 100, 250, and 500 msec inter-stimulus interval (ISI) were presented in random order. The model was useful in predicting the magnitude of the age difference in RT and the difference in RT between the 50 and 100 msec ISI. However, old subjects were not disproportionately slowed at the 100 msec ISI as the model would predict and all RTs were underestimated. Thus, while a model using EEG alpha period and RP to predict age differences in RT has some weaknesses, it is useful enough to warrant additional examination.