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Transgenerational plasticity occurs when the conditions experienced by the parental generation influence the pheno-type of their progeny. This may in turn affect progeny performance and physiological tolerance, providing a means by which organisms cope with rapid environmental change. We conditioned adult purple sea urchins, Strongylocentrotus putpurams, to combined pCO(2) and temperature conditions reflective of in situ conditions of their natural habitat, the benthos in kelp forests of nearshore California, and then assessed the performance of their progeny raised under different pCO(2) levels. Adults were conditioned during gametogenesis to treatments that reflected static non-upwelling (similar to 650 mu atm pCO(2), similar to 17 degrees C) and upwelling (similar to 1300 mu atm pCO(2), similar to 13 degrees C) conditions. Following approximately 4 months of conditioning, the adults were spawned and embryos were raised under low pCO(2) (similar to 450 mu atm pCO(2)) or high pCO(2)(similar to 1050 patm pCO(2)) treatments to determine if differential maternal conditioning impacted the progeny response to a single abiotic stressor: pCO(2). We examined the size, protein content, and lipid content of eggs from both sets of conditioned female urchins. Offspring were sampled at four stages of early development: hatched blastula, gastrula, prism, and echinopluteus. This resulted in four sets of offspring: (1) progeny from non-upwelling-conditioned mothers raised under low pCO(2), (2) progeny from non-upwelling-conditioned mothers raised under high pCO(2), (3) progeny from upwelling-conditioned mothers raised under low pCO(2), and (4) progeny from upwelling-conditioned mothers raised under high pCO(2). We then assessed the effects of maternal conditioning along with the effects of developmental pCO(2) levels on body size of the progeny. Our results showed that differential maternal conditioning had no impact on average egg size, although non-upwelling females produced eggs that were more variable in size. Maternal conditioning did not affect protein content but did have a modest impact on egg lipid content Developing embryos whose mothers were conditioned to simulated upwelling conditions (similar to 1300 mu atm pCO(2), similar to 13 degrees C) were greater in body size, although this effect was no longer evident at the echinopluteus larval stage. Although maternal conditioning affected offspring body size, the pCO(2) levels under which the embryos were raised did not. Overall, this laboratory study provides insight into how transgenerational effects may function in nature. The impacts of parental environmental history on progeny phenotype during early development have important implications regarding recruitment success and population-level effects.