Axenic Entamoeba histolytica cultures, grown in PEHPS medium, showed increasing yields and growth velocity when added with 0.03 to 0.6 g/l gallbladder ox bile, while higher doses were toxic for amebas. The highest density (505 +/- 29 x 10(3) trophozoites/ml) and shortest duplication time (Dt = 10.74 +/- 0.2 h) corresponded to cultures added with 0.24 g bile/l. Their yields were 1.74 and 3.34 times higher, respectively, than those which were reached by the non-added PEHPS controls and by growth of amebas in TYI-S-33 medium. Between 72 and 96 h of incubation a noticeable increase in trophozoite density was observed in cultures added with 0.24 g/1 bile among controls. At 72 h yields of bile-added cultures inoculated with 5, 10 and 20 x 10(3) amebas/ml increased in function of the inoculum. The improved growth of E. histolytica by adding 0.24 g/l ox bile to culture medium suggests that bile has compounds are essential for amebas.