A strain of Rhizopus stolonifer produced high levels of extracellular ribonuclease (RNase) when grown on YPG (yeast extract, peptone, glucose) medium. Influence of various medium components on the production of extracellular RNase activity showed that divalent metal ions had a marked effect on growth and enzyme production, Maximum enzyme activity (3000 U/ml) was obtained in 5 days when the culture was grown in YPG medium containing Mg2+ (12 mM), Mn2+, and Fe2+ (2 ppm each), Inorganic phosphate, however, repressed enzyme production, Antibodies raised against the purified extracellular RNase were then used to establish the relationship between intra- and extracellular enzymes.