The effect of different levels and combinations of Ca and P consisting of nine treatments as Ca_oP_o, Ca_r, P_r, ~, P_d, (CaP)_r, Ca_dP_r, (CaP)_d and Ca_rP_d 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 (P_i) 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 P_i concentration was significantly affected by treatments. Serum Ca and P_i are negatively correlated (r = -0,5307). Ca_r resulted in the highest concentration of serum Ca but depressed serum P_i more effectively than e.g. Ca_oP_o and Ca_d. 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 P_i and VFA were found to be significantly associated as well as rumen Ca with VFA and TCA-N, respectively.