Young land-snails (Cochlicella ventricosa) were infested with a plurigeneric mixture of first-stage larvae of Protostrogylids. Cochlicella ventricosa is good host for Cystocaulus and Neostrongylus. Only one larva is able to ensure its complete evolution at a first infestation. A second larva follows the same process, at a second infestation. Such a regulation of the infestation recalls the limitation phenomenon. Hypothesis concerning this regulation process are discussed.20