Using a modified crystal violet sodium polypectate (CVPB) double layer medium with 2,3,5-triphenyltetrazolium chloride and L-asparagine in the basal medium and bromthymol blue in the upper, both containing tryptone, gave red to pink colonies of Erwinia carotovora ssp. carotovora on a blue green background with cavity formation. The addition of 1.2 μg/ml polymyxin B sulphate to the upper layer inhibited the growth of Erwinia carotovora ssp. atroseptica, while 32 μg/ml erythromycin in the upper layer inhibited the growth of E. chrysanthemi. The addition of 35 μg/ml novobiocin inhibited the growth of Bacillus sp. Non-target bacteria such as Pseudomonas fluorescens, P. marginalis, Ralstonia solanacearum and E. herbicola formed pink, red, yellowish or white colonies without cavity formation. The growth of non-target bacteria on the semi-selective medium was one tenth of that obtained using CVPB medium. Copyright © 2005 Whurr Publishers Ltd.