The activity of β-galactosidase during incubation of soil with lactose was studied. Enzyme activity reached its maximum between 6–24 h incubation. The addition of secondary ammonium phosphate stimulated the enzyme formation. Casein hydrolysate alone did not influence significantly enzyme formation even after a 72 h incubation. Enzyme activity in the non-incubated soil was also insignificant. Glucose added to the soil incubated with lactose decreased the formation of the enzyme.