This study evaluates the developmental toxicity of two high molecular weight dialkyl phthalate esters, diundecyl phthalate (DUDP) and ditridecyl phthalate (DTDP). Sprague-Dawley rats were administered 0, 0.25, 0.50, or 1 g/kg/day of DUDP or DTDP, by gavage, on gestation days 6-20. DUDP and DTDP had no adverse effects on maternal body weight and food consumption. The number of live fetuses, percent of post-implantation loss and of resorptions, fetal sex, and fetal body weights were not affected by either phthalate. There was no evidence of teratogenicity, whatever treatment. Small decreases in the anogenital distance of male fetuses were noted at 0.5 and 1 g DUDP/kg/day. The incidence of fetuses with supernumerary lumbar ribs was significantly higher than control at 0.5 and 1 g DUDP/kg/day. Thus, DTDP was not developmentally toxic up to 1 g/kg/day and there were signs of DUDP-induced fetal effects at 0.5 and 1 g/kg/day. (C) 2013 Elsevier Inc. All rights reserved.