ABSTRACTConditions optimal for assay of staphylococcal nuclease were established by spectrophotometric measurement of acid soluble oligonucleotides produced from heat denatured calf thymus deoxyribonucleic acid (DNA) by purified micrococcal nuclease (DNase, E.C. No. 3.1.4.7) as well as crude DNase fromStaphylococcus aureus. Assay conditions of 50°C. calcium concentration of 0.005M, NaCl concentration of 0.17M and pH of 10.0 were optimal for activity of DNase. There was a sixfold increase in activity of DNase under these conditions over that observed under the most commonly used assay conditions of 37°C and pH 9.0. Use of 50°C and pH 10.0 in a DNA‐agar diffusion system also resulted in a reduction in assay time by twofold with crude DNase from growth of weak or strong DNase producing strains ofS. aureus. Similarly, the assay time of DNase extracted from dried malted milk and cheddar cheese (involved in staphylococcal food poisoning) was also reduced by twofold at 50°C and pH 10.0 over that observed at 37°C and
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