The aim of the study was to determine bioavailability of some mineral components – calcium and phosphorus from diets containing acid permeate and acid rennet permeate obtained as tvorog production by-products. Bioavailability of minerals was determined by balance method, using growing Wistar rats and expressed by apparent absorption (A) and apparent retention (R ) indices, on the base of calcium and phosphorus intake and their fecal and urinary excretion. The diets were composed in such a way as to ensure that permeate constituted the only source of a given mineral component in any diet (addition of a proper mineral mix). Permeate, diets, excrements and urine were wet ashed and then tested for calcium content by ASA method with the help of an atomic absorption spectrofotometer, while the level of phosphorus was determined by colorimetric method. Statistical differences between values of calcium A and R indices for both permeate were observed. The results confirmed the higher apparent absorption and apparent retention of calcium and phosphorus from acid and rennet permeate than from acid one. The way of milk coagulation significantly influenced on bioavailability of calcium and phosphorus from diets containing the tested permeates. The results indicate that acid rennet permeate can be recommended to fortification of food in the calcium and phosphorus. Permeate should therefore be used commercially as a valuable source of highly available elements.