Lipases (triacylglycerol hydrolases) are hydrolytic enzymes that can catalyze the hydrolysis of the ester bond of long-chain acylglycerols at the oil-water interface. The present study investigated the effects of inducers, surface-active materials, activators, and inhibitors in the fermentation medium on lipase activity in Rhizopus delemar. In the presence of certain commercial oils and tributyrin as an inducer, lipase activity decreased in the order of sunflower oil > soybean oil > hazelnut oil > corn oil > tributyrin > olive oil. In addition, the effects of the stirring and aeration rates on lipase activity were investigated. To investigate the effect of surface-active materials on lipase activity 2 different surface-active materials, Tween-80 and rhamnolipid (biosurfactant), were used as comparatives with tributyrin. Maximum lipase activity was observed in the fermentation medium containing Tween-80 as both an inducer and surface-active material. The combined effects of molasses and sucrose on lipase production by R. delemar were also investigated. Lipase activity in the presence of activators decreased in the order of NaCl > KCl > CaCl(2) > MgCl(2) > gum arabic > EDTA, and maximum lipase activity of 964.55 U/L was obtained. The presence of heavy metal ions in the fermentation media severely inhibited lipase activity. Lipase activity in the presence of heavy metal ions decreased in the order of Fe(2+) > Mn(2+) > Co(2+) > Ni(2+).