SUMMARY.In this study we have tested for the first time the susceptibility of Ponentina ponen tina, Euomphalia (M.) brigantina, Oestophora (O.) barbuta, as potencial intermediate hosts of Muellerius capillaris. At the same time, the development of the above mentioned parasite in Cepaea nemoralis and Helix (C.) aspersa was followed.The total number of molluscs used in the infections was 268. The dose of M. capillaris L-I used ranged between 65 and 838 larvae per mollusc. Once the snails had been infected, 1 or 2 examples from each species were killed every day between day 6 and 46 post-infection, to study the larval development of the parasite.In order to define the suitability of the molluscs as intermediate hosts for this parasite, the number of L-I that penetrated the foot of each snail and developed to L-II and L-III has been taken into account, as well as the first day on which the different stages were observed.The analyses of variance (one way) showed statistically significant differences among the species of molluscs tested, concerning the percentages of penetration, total amount of larvae and L-III. The correlation coefficient showed that there was a relationship between the last two per centages.According to our results the species: C.