Plasma vitellogenin and 17 beta-estradiol concentration were determined during the annual reproductive cycle of the female lizard Podarcis s. sicula Raf. living around Naples. Plasma vitellogenin was purified from estrogenized males for characterization and to raise specific immune serum. Using ELISA, plasma vitellogenin titers were determined in relation to ovary weight; plasma 17 beta-estradiol was measured by RIA method. Native vitellogenin was present as two polypeptide bands: alpha and beta. The electrophoretic patterns, studied in normal male and estrogenized male and female, showed vitellogenin to be a protein present in female and in estrogenized male plasma but not in normal males. Lizard monomeric VTG, determined by SDS-PAGE, was about 200 kDa. Correlations between seasonal ovarian weight variations and plasma vitellogenin and 17 beta-estradiol suggest that ovarian development in Podarcis depends on plasma vitellogenin synthesis, which in turn relies on plasma estradiol levels. The two ovulatory waves observed in this study coincided with the two peak values of plasma vitellogenin and 17 beta-estradiol.