Purchase probability as a function of interpurchase time was examined through comparison of findings from laboratory experiments on reinforcement schedules and from marketing investigations of consumers' interpurchase time. Panel data, based on a sample of 80 consumers who purchased nine supermarket food products during 16 weeks, were used. For each product category, interpurchase time was similar for each shopping occasion and cumulative purchase probability increased as a Gamma function of the time since the last purchase. A comparison of interpurchase times across products and consumers showed that average interpurchase time differed across four subsets of products and across seven groups of consumers, with a significant interaction effect. Interpurchase times tended to be longer after larger purchases, as would be predicted from laboratory results. A correlation between individual interpurchase time and number of products bought on each shopping occasion indicated that consumers who shop more frequently buy larger numbers of products per occasion. These results have several managerial implications and demonstrate the usefulness of a behavior-analytic framework in the interpretation of consumer behavior.The concept of reinforcement is central to operant theory. When interpreted as an operation rather than a process, it has been usually defined as the delivery of a reinforcer when a response occurs (Catania, 1998;Skinner, 1953). A reinforcer, in turn, is commonly defined as any event that when produced by a response increases its likelihood under similar conditions. So, by definition, reinforcement of a response increases the probability of the response occurring under similar circumstances. When events that function as reinforcers for certain organisms under certain conditions are identified, for example, food for J. M. Oliveira-Castro thanks the Brazilian institutions CAPES (Ministry of Education),