The effect of different levels and combinations of Ca and P consisting of nine treatments as CaoPo, Car, Pr, ~, Pd, (CaP)r, CadPr, (CaP)d and CarPd were investigated with an unrestricted semi-purified diet (r= to the rumen; d = to the duodenum, and 0 = no supplementation). P supplementation, irrespective of site, depressed Ca absorption and retention and vice verca. P absorption is favoured by high oncentrations in the duodenum, absorption thus being concentration dependent. Ca and inorganic P (Pi) concentration in rumen liquor is intake dependent; the former more so than the latter. The serum Ca was relatively stable despite treatment differences, whereas serum Pi concentration was significantly affected by treatments. Serum Ca and Pi are negatively correlated (r = -0,5307). Car resulted in the highest concentration of serum Ca but depressed serum Pi more effectively than e.g. CaoPo and Cad. The Ca and P maintenance requirements were found to be 3,0 and 1,8 g/day and the endogenous loss 0,5 and approximately 0,34 g/day respectively. The Ca/P ratio for the rumen microorganisms is not critical but the rumen Ca level may usually be of a more critical nature in contrast to rumen Pi levels, and thus, favouring a wider ratio than is usually recommended for non-ruminants. Concentrations of rumen liquor Pi and VFA were found to be significantly associated as well as rumen Ca with VFA and TCA-N, respectively.