Epidemiological studies indicate that high intakes of fruits and vegetables are associated with a reduced risk of cancer, and several plant-derived drugs have been developed in medical oncology. Since only a small part of the flora has been tested for any kind of bioactivity, we chose small fruits as sources of differentiation-inducing activity against HL-60 leukemic cells. We have prepared juices from various small fruits that grow mainly in the northern part of Japan. Screening of 43 samples indicated that juices of Actinidia polygama Maxim., Rosa rugosa Thunb.,Vaccinium smallii A. Gray, and Sorbus sambucifolia Roem. strongly induced differentiation of HL-60 Cells to monocyte/macrophage characteristics in a concentration-dependent manner as indicated by histochemical and biochemical examinations.