The Organisation for Economic Cooperation and Development is promoting the development and validation of mollusc toxicity tests within its test guidelines programme, eventually aiming for the standardization of mollusc apical toxicity tests. Through collaborative work between academia, industry and stakeholders, this study aims to develop innovative partial life-cycle tests on the reproduction of the freshwater gastropods Potamopyrgus antipodarum and Lymnaea stagnalis, which are relevant candidate species for the standardization of mollusc apical toxicity tests assessing reprotoxic effects of chemicals. Draft standard operating procedures (SOPs) have been designed based upon literature and expert knowledge from project partners. Pre-validation studies have been implemented to validate the proposed test conditions and identify issues in performing the SOPs and analyzing test results. Pre-validation work for P. antipodarum consisted in a comparative 28-day study between four laboratories and with two test substances: cadmium (Cd) and bisphenol A (BPA). For L. stagnalis, pre-validation consisted in a comparative 56-day study between six laboratories and with two test substances: Cd and tributyltin (TBT). Cumulated fecundity per individual over the test period was SETAC 6th World Congress/SETAC Europe 22nd Annual Meeting 223 the main test endpoint. Tested animals came from a single laboratory culture (i.e. the University of Frankfurt for P. antipodarum and INRA for L. stagnalis). Snails were acclimated in partner laboratories and exhibited homogenous age and size at the beginning of the tests. All laboratories found a concentration-dependent decrease of fecundity in both species under Cd exposure. Values of NOECs and LOECs were generally homogenous among laboratories. Results of the pre-validation studies with P. antipodarum and L. stagnalis exposed to Cd are thus very encouraging. Results for BPA highlighted issues in controlling exposure concentrations, and possibly BPA leaching from test equipment. This study also highlighted that factors, such as e.g., snail origin, temperature and test chemical stability in water, must be controlled in mollusc toxicity tests to avoid data dispersion which may impede the interpretation of effects. Applicability and limitations of the SOP proposed for L. stagnalis will be assessed after completion of the on-going pre-validation work. In both cases, optimization of experimental conditions and test procedures is required before the SOPs are ready to be proposed as OECD test guidelines.