In this study, embryotoxic and genotoxic effects of nonylphenol (NP) and octylphenol (OP), which are the derivates of alkylphenol (APs), were evaluated using the gametes and embryos of the sea urchin Paracentrotus lividus. The sperm and eggs of sea urchins were exposed to increasing concentrations of NP (0.937-18.74 mu g/L) and OP (5-160 mu g/L) under static conditions. The endpoints were sperm fertilization success, quantitative and morphologic changes in mitotic activity, larval malformations, developmental arrest, and embryonic/larval mortality. A dose-response-related reduction (approximately 20%) was observed in fertilization success and significant increases in the number of larvae with skeleton malformations at the pluteus stage of the contaminated sperms. The spermiotoxic and embryotoxic concentrations were determined as 0.937 mu g/L for NP and 4.685 mu g/L for OP for this species. The embryotoxicity of NP and OP is concentration dependent, and significant growth reduction at the early life stages and an increase in larval malformations as skeleton deformities at the pluteus stage were observed. Cytogenetic analysis of embryos showed a decreasing curve in mitotic indexes (number of mitosis per embryo) with increasing concentrations of NP and OP. It can be concluded that NP and OP adversely affect the reproduction and embryonic developmental stages of the P. lividus and this is of great ecological importance because of the hazard at the population level.