The study describes the sorption of Cr, Cu, Mn and Zn by Pseudomonas aeruginosa AT18 isolated from a site contaminated with petroleum and heavy metals. The concentrations studied were 50, 49, 60 and 70 (mg L(-1)) for Cr, Cu, Mn and Zn, respectively. The solution pH and ionic strength were very important factors in the metal biosorption performance and the biosorption capacity of A aeruginosa AT18 for Cr(3+), Cu(2+), Mn(2+) and Zn(2+). In aqueous Solution, the biosorption increased with increasing pH in the range 5.46-7.72. The results obtained in the experimental assays show that A aeruginosa AT18 has the capacity for biosorption of the metallic ions Cr(3+), Cu(2+) and Zn(2+) in solutions, although its capacity for the sorption of manganese is low (22.39 mg Mn(2+)/g of biomass) in comparison to the Cr(3+), Cu(2+) and Zn(2+) ions, as shown by the individual analyses. However, 20% of the manganese was removed from an initial concentration of 49.0 mg L(-1), with a Q(m) value similar to that obtained in solutions containing mixtures of Cr(3+), Cu(2+). Mn(2+) and Zn(2+). The chromium level sorbed by P. aerugirrosa AT18 biomass was higher than that for Cu, Mn and Zn, with 100% removal in the pH range 7.00-7.72 and a Q(m), of 121.90-200.00 mg of Cr(3+)/g of biomass. The removal of Cr, Cu and Zn is also a result of precipitation processes. (C) 2008 Elsevier Ltd. All rights reserved.