In vitro effects of C. nervosum (1A), G. pentaphyllum (1B), H. suaveolens (1C) and P. grandifora (1D) on NK activity. PBMC were cultured in the presence and absence of different concentrations of each extract for 18 hrs. NK cell activity was determined by culturing stimulated PBMC with 51Cr-K562 cells in triplicate at different E:T ratios for 4 hrs at 37oC. Supernatants were counted for radioactivity and % lysis calculated. Each bar represents mean±SD. *p< 0.05