The effects of eight kinds of Chinese medicinal herbs (CMH) on human lymphocytes was studied in vitro. The extract of Cinnamomum cassia presl markedly stimulated human lymphocytes to proliferate. Codonopsis pilosula, Oldenlandia diffusa and Rhizoma typhonii weakly stimulated. These extracts enhanced cytotoxic T-lymphocyte (CTL) activity, but failed to enhance natural killer (NK)-cell activity. The extracts of these CMHs have stimulatory effect on immunoglobulin (Ig) production by B-cells and interleukin(IL)-1 production by monocytes. These activities of Cinnamomun cassia presl extract are associated with glycoproteins, whose molecular weight was about 100 KDa. These results suggest that CMH extracts have a stimulating activity on human lymphocytes and these abilities could be used clinically for the treatment of diseases such as cancer.