The development of potentiometric biosensors for creatinine based on creatinine iminohydrolase (E.C. 3.5.4.21) immobilized on chitosan membranes coupled to a nonactin based ammonium ion selective electrode is described. The response characteristics of three types of biosensors with the enzyme immobilized by three different procedures were evaluated. The biosensors with better response characteristics were obtained by coupling the ammonium ion selective electrodes to chitosan membranes with the enzyme immobilized by adsorption. The linear response range of these biosensors to creatinine was 10(-4) to 10(-2) M, the response time was between 30 and 60 s, they showed an operational lifetime of 44 days and the slope of the response to creatinine in the first day varied between 50 and 52 mV decade-1. An array of six potentiometric sensors, constituted by two creatinine biosensors and four ion selective electrodes for potassium, sodium, ammonium and calcium was calibrated and a multivariate model based on PLS1 for the response to creatinine was obtained and validated. The array was used for the analysis of creatinine in urine samples and the results were compared with the results of a clinical analysis laboratory, based on the Jaffé reaction.