In poultry production, the washing stage takes place after the gutting stage. In the washing stage the carcasses are cleaned with pressurised water in order to remove any remains of blood, dirt and feathers on the skin, to reduce the superficial contamination, and to avoid subsequent drying in the freezers. This step is an important phase in the productive line because of its usefulness and its cost, since water is an expensive product and, sometimes, in short supply. Total Count, Pseudomonas, Enterobacteriaceae and Slaphylococcus are microbial groups frequently analysed on carcasses in slaughterhouses. Their usefulness as index of microbiological quality can be assessed by means of univariate and multivariate statistical methods. In this study the influence of the washing stage on the superficial contamination of the chicken carcasses is shown with regard to the following factors: the water pressure, the amount of water and the length of the washing stage. It makes clear that multivariate statistics appears as a valuable tool for designing and implementing quality control systems, demonstrating that the contamination decreases significantly due to the effect of the washing stage and the water pressure. Time and amount of water variations do not affect the microbiological variables except for the Pseudomonas, which are affected by the amount of water and time variation but not by pressure variation. (c) 2004 Elsevier Ltd. All rights reserved.