In Tenerife, Canary Islands, a complex infrastructure exists, whose aim is the reuse of wastewater for crop irrigation. For this reason, techniques of advanced treatment, such as micro-ultrafiltration, have been developed. A laboratory-scale study was carried out to evaluate the feasibility of a combined process of coagulation-flocculation with filtration through hollow-fibre membranes as tertiary treatment of the effluent of a conventional activated sludge plant. The Aluminium Polychloride (AIP) was tested as coagulant-flocculant and a hollow-fibre membrane module of rated pore diameter of 0.03 mum and filtering surface of 0.093 m(2), supplied by Zenon Environmental, was used. The water resulting of the flocculation step was filtered by the hollow-fibre. The experiments were carried out in absence of air, without permeate backwash and without maintenance cleaning. In this study, concentrations of 5, 10, 20 and 30 mg/l of AIP and permeate flow-rates of 4.5, 5.9 and 8.5 l/h have been tested. The evolution of membrane fouling, expressed as the variation of transmembrane pressure, shows the clear advantage of the feedwater pretreatment. From the economical and technical point of view, the optimal concentration is 10 mg/l of AIP.