Agrobacterium transformation systems for Brassica, Solanum and Rubus, using carbenicillin, cefotaxime and ticaracillin respectively to eliminate contamination, were examined for the presence of residual Agrobacterium. The results indicated that none of the antibiotics in question, succeeded in eliminating Agrobacterium and the contamination levels increased in explants from 12 to 16 weeks to such an extent that Solanum cultures senesced and died. This may be due to the fact that four times the Minimum bactericidal concentration values (concentration to be used for elimination of contaminants in culture), for the three antibiotics, were higher than the concentrations employed in the culture medium. Contamination in shoot material decreased over 16 to 24 weeks possibly due to bacteriostatis and the use only of the apical node for further culture. The presence of the binary vector was also noted under non-selective conditions, even up to 6 months after transformation, where approx. 50% of contaminated material still harboured bacterial cells with the binary vector at levels of approx. 107 Colony forming units per gram.Abbreviations: CFU -colony forming units, GUS -fl-glucoronidase, PCR -polymerase chain reaction, MBCminimum bactericidal concentration, NPTII -neomycin phosphotransferase, RAPD's -random amplified polymorphic DNA