Summary -pH-lnduced physicochemical changes and rennet coagulation times of casein micelle suspensions have been studied with native phosphocaseinate powder dissolved in water, 0.1 mol L-1 NaCI and milk ultrafiltrate. An increase in ionic strength between water and NaClled to higher diffusible calcium and phosphorus, to greater micelle voluminosity and to greater case in and minerai solubilization during acidification. Dissolution of the phosphocaseinate in ultrafiltrate resulted in physicochemical properties very close to milk. The acidification process can be divided into five successive steps. Relations between physicochemical changes are discussed, together with the reduction of rennet coagulation time with pH and ionic strength reduction.