The Procedure for pyocin typing of Pseudomonas aeruginosa isolations as proposed by GILLIES and GOVAN has been modified in the following aspects: strains are arranged in a symmetrical way, with a central producer zone and radial indicator streaks, optimal size of inocula for both producer (300 x 10(6)/ml) and indicators (50 X 10(6)/ml) was determined, unsupplemented Tryptic Soy Agar is used giving identical results to those when TSA is supplemented with 5% horse blood. The typing results obtained with this simplified and standardized procedure were identical with those from the cross streak method.