4 experiments in simple and choice reaction time (RT) are reported. Experiment I examines the effect of monetary payoffs on the accuracy and variability of time estimation. Experiment II examines the effect of moving the position of a narrow payoff band along the time axis on the variability of observed RTs. This appears to alter the proportion of bona fide reactions (of low variability) and of more variable time estimates of the foreperiod duration. Experiment III is designed to assess the factors responsible for the increased mean and variability of choice compared with simple RT distributions. It is concluded that information processing rather than motor factors is primarily responsible for the difference between simple and choice RT. Experiment IV studies the relation between RT of correct and error responses as a function of variations in stimulus probability in a 2-choice RT paradigm. Finally, several theoretical distributions are evaluated by the empirical distributions obtained in Experiments II, III, and IV; none seems wholly satisfactory, but those with rounded modes and an exponential tail (e.g., the gamma) are clearly not adequate. (PsycINFO Database Record (c) 2006 APA, all rights reserved)