The isolation of Streptomyces can be facilitated by addition of the following antibiotics to the plating medium: actidione 20[mu]/ml, polymyxin 20[mu]/ml, subtilin 20[mu]/ml, and penicillin 2.5[mu]/ml. For isolation of fungi, another combination of antibiotics is recommended, i.e., penicillin 5[mu]/ml, streptomycin 10[mu]/ml, polymyxin 40 [mu]g/ml, bacitracin 20 [mu]g/ml, and Aureomycin 20[mu]/ml. The radial growth of rapidly spreading fungi is restricted by use of 0.03% sodium desoxycholate.