Human monocytes were separated from peripheral blood of 22 normal healthy adults and incubated with Hsw1N1 influenza virus or diluted allantoic fluid. The treated monocyte populations were tested for five parameters of monocyte function. Influenza infection markedly inhibited the monocyte chemotactic response and the killing of Candida albicans; infection also depressed phagocytosis, slightly reduced spreading, but did not affect adhesion to glass. These results suggest that influenza virus may also have an inhibitory effect on monocyte function in vivo and help to explain the increased susceptibility to secondary bacterial infection and the general immunosuppression seen in influenza infection.