According to the nature of the run of stimuli and outcomes, either positive or negative recency may be exhibited in the initial responses to a two-choice guessing task. When red and black two-digit numbers printed in two columns were used as stimuli, subjects responded to a run on one colour with positive recency, but to a run on one column with negative recency. Responses were found to be related to prior expectations in a way which occurs with a rational Bayesian decision process. With a very long run on one position (either column) the marked negative recency which occurred initially eventually gave way to positive recency. Three experiments are reported.