The olfactory learning capability of the male cockroach Periplaneta americana was studied using an operant discriminatory conditioning paradigm. Cockroaches were highly motivated to search for a sucrose solution by giving them a diet that contained no sugar and by limiting their water supply, and they were individually trained to associate peppermint with sucrose solution and vanilla with NaCl solution. Their odor preference was tested before and after training by allowing them to choose between peppermint and vanilla sources. The time spent visiting each odor source served as a measure of odor preference. Cockroaches exhibited an innate preference for vanilla over peppermint but the preference for the latter increased after only one training session. The olfactory memory formed by a single training session remained for at least one week but significantly decayed from 2 to 24 hr after training. Memory formed by three training sessions was extremely robust, exhibiting no significant decay from one day to four weeks after training. The preference formed was easily altered by reversal training in which vanilla was associated with sucrose solution and peppermint with saline. This study shows that cockroaches have an excellent olfactory learning capability characterized by rapid acquisition, extremely long retention and easy re-writing of memory.