Prefrontal cortex plays an important role in the acquisition and retention of working memory. To address working memory for multiple concurrent items, monkeys were trained with a foraging task in which animals explored a choice array, searching for a number of rewarded target locations, and remembered these locations once they were found. A circular array of four to eight choice locations, marked by white squares, was presented on a touch panel display with an initial fixation point (FP). Each trial started when the animal held a home key and fixated the FP for 1-2.5 sec, then the animal released the home key and touched one of the choice locations when FP changed in color. After 350-450 ms of touch-hold period, the color of the selected location changed to green or red, revealing that the location was a target or a non-target, respectively. When a target was selected, a drop of soft food was given as a reward. The number of the targets was one to three and the trials were repeated until the animal had touched all the target locations, then a cycle of foraging trials ended. The end of each cycle was indicated by blinking the target array. Then cycles with the same targets were repeated three to five times to form a set of cycles. When a new set started, the animals searched targets efficiently with few repeated touches on the same locations in the first cycle (exploration phase). After the initial exploration, their performance improved quickly, with almost no error touches in the later cycles (memory phase). While animals performed the foraging task, we recorded single unit activities in the dorsolateral prefrontal cortex (DLPFC). We found many neurons showing different target selective activities in the first cycle from those in the repeated cycles, some firing vigorously in the first cycle and others not. There were also neurons specifically firing after the identity of the touched location was revealed in the first cycle, but little sustained activity carrying target information from one touch to the next. These activities may be related to the acquisition of working memory.