Validated guidelines in line with the OECD Conceptual Framework for the Testing and Assessment of Endocrine Disrupting Chemicals (EDTA) have been developed for rodents, amphibians, fish, aquatic insects and crustaceans. Only aquatic arthropods have been considered in this test battery although the comparison of endpoints relevant for reproduction in invertebrates often shows a much higher sensitivity in molluscs vs. e.g. daphnids. The OECD test guideline programme has thus been extended to cover reproduction effects of chemicals in molluscs. Existing mollusc toxicity test protocols have been reviewed in an OECD Detailed Review Paper that identifies two relevant candidate species for developing freshwater tests: Potamopyrgus antipodarum and Lymnaea stagnalis. However, this review did not clarify which toxicity test design/conditions are the most appropriate for chemicals assessment. Therefore, a mollusc reproduction test guideline will be developed describing partial- and full- life-cycle test protocols in these species, so as to propose a balanced suite of apical mollusc toxicity tests applicable for the assessment of any type of chemical, including endocrine disruptors, as level 4 and 5 assays of the EDTA Framework. The guideline project is led by a consortium of experts (Germany/United- Kingdom/France/Denmark) from academia, industry and government stakeholders. To date, expert knowledge has been gathered and formed the basis of draft standard operating procedures (SOPs) for the culture and test implementation of the partial life-cycle tests in both species. Prevalidation of these SOPs consisted in two ring-tests involving 10 partner labs with different level of expertise in mollusc tests. Effects of cadmium on the individual reproductive outputs were studied over 28-d in P. antipodarum and over 56-d in L. stagnalis. Pre-validation tests were successful in both species. Indeed, both species could be successfully cultured at the lab. Toxicity tests provided consistent results among laboratories for each species (e.g. homogenous and nonsignificantly different NOECs, LOECs and EC 50 values for most partner labs). The draft SOPs will be optimized (e.g. statistical tests showed that the duration of the test with L. stagnalis can be shortened to from 56-d to 35-d) and further tested for various types of reproductive toxicants including endocrine disruptors. A broad scale ring-test will be conducted in 2014 for both species based upon the consolidated SOPs.