Responses of plants to abiotic stress include the synthesis of osmolytes, low-molecular-weight metabolites that are able to compensate high osmotic pressure without interfering with plant metabolism, even at elevated concentrations. They include some sugars, polyols, amino acids and quaternary ammonium compounds. Proline is a typical osmolyte, synthesised by plants under different environmental stress conditions. In the present study, levels of proline in several xerophytic Mediterranean species were determined in plants collected in the wild, in winter and spring of 2009, in a semi-arid area near Valencia, Spain. Total sugar content was also determined in the same plant samples. The results obtained showed a general reduction in both, sugar and proline contents from winter to spring sampling, probably due to the heavy rains registered in early spring, which reduced the environmental stress. The species with higher levels of proline, contained generally less sugars, and vice versa; this finding is consistent with previous data indicating that any particular species normally accumulates only one type of osmolyte in significant amounts. No correlation was found between levels of proline and the taxonomy of the investigated species.