The effect of growth conditions on urease synthesis was studied with Staphylococcus saprophyticus L-1 isolated from natural sources. Urease biosynthesis was recorded in the absence of urea in the complete medium and in the conditions of nitrogen deficiency; the highest level of the enzyme biosynthesis was found when the culture was grown in the absence of amine nitrogen in the medium. Ammonium ions were a reversible inhibitor of urease and, at a high concentration (30 g of (NH4)2SO4 per litre of the medium), partly repressed its biosynthesis. The rate of growth was low when the cells were cultivated in flasks in a medium containing urea (20 g per litre of the medium). The growth was not inhibited when the cells were cultivated in 20-litre fermenters at the same concentration of urea, but with automatic pH regulation. The alkaline medium rather than urea contained in it appeared to be the principal factor inhibiting growth of the culture.