The influence of three salts (KN03, NH4N03 and (NH4>2S04) in different concentrations, on the growth and mineral composition of olive seedlings cultured in vitra and in greenhouse conditions, was studied. The best growth was obtained in in vitra culture through the applications of NH4N03, in concentrations of 10 and 20 mM of N. Addition of (NH4)2S04 clearly damaged the seedlings and increased the contents of S in the seedlings' tissues. AH the treatments led to a direct relationship between concel'ltration of N in the medium and N in the seedling tissues, however the N-increases were lowest for KN03 and highest for ammonium applications, especiaHy for NH4N03. In greenhouse conditions aH the N-treatments significantly increased the growth of the seedlings but no significant differences between N-salts were observed except for (NH4)2S04 at the highest concentration. Treatment with (NH4)2S04 did not induce any symptom of toxicity in the seedlings, in contrast to the behaviour of in vitro seedlings. The treatments did not cause significant changes in the mineral composition of the seedling tissues. These circumstances were related to the fact that an oxidation process (nitrification) was produced from N-NH4 to N-N03 in the nutritive solutions in the containers.