Previous studies show that the LP-BM5 murine leukemia virus causes an acquired immunodeficiency syndrome in C57BL/6 mice (MAIDS) and impairs learning and memory without gross motor impairment. To assess spatial working memory impairment after LP-BM5 infection and the time course of this impairment, we tested mice in a modified working-memory version of the Morris water maze. Twenty mice were inoculated with LP-BM5; controls received medium (Minimum Essential Medium). In the test procedure, animals had two 1-min training sessions to learn the position of a randomly placed hidden platform. Thirty seconds after the second training session, animals were placed in the maze without the platform, and time and pathlength spent in each quadrant of the maze were measured. For 9 weeks after LP-BM5 infection, both groups showed preference for the target quadrant compared to the opposite quadrant. At 10 and 11 weeks after infection, the LP-BM5 virus infected mice lost this target quadrant preference. We conclude that LP-BM5 infection impaired spatial working memory in a modified working-memory version of the Morris water maze test in C57BL/6 mice at 10 and 11 weeks after virus infection.