African Giant Snails (Achatina fulica) about 6 weeks old were experimentally infected with each 5,000 to 20,000 first stage larvae of Angiostrongylus vasorum or A. cantonensis by exposure to a larval suspension. The snails were histologically examined after various intervals after infection: 1 hour post infectionem (p.i.) larvae were present in the foot and 2 hours p.i. in addition in the gastrointestinal tract. 12 hours p.i. larvae were seen for the first time in the lung which reached nearly half of the total number of larvae via the hemolymph system. 24 hours p.i. or later 80-90% of the total larval population were detected in the foot and the lung. In the various organs (lung, mantle, hepatopancreas, gastro-intestinal tract, foot) the larvae were found in the loose connective tissue near or within the hemolymph vessels. The cellular defense mechanism of the snail is activated 12 hours p.i. and the parasites are surrounded by large numbers of leucocytes (leucocytic encapsulation). Three days p.i. the nuclei of the cells become spindle shaped and are forming concentric layers in the outer part of the capsule (fibroblastic type of encapsulation). Later on the wall of the encapsulation becomes thinner and a karyolysis can be recognized in the centre, consequently a cavity occurs. Encapsulations in organs poor in muscle cells can histologically not be differentiated from those located in the foot, which consists mainly of muscle cells; a myofibrous type of encapsulation has to be doubted. The effects of the infection on the snail are discussed.