1. The olfactory orienting behavior of the terrestrial snailAchatina fulica was studied in intact animals, in animals with bilateral lesions of either the anterior tentacles or the posterior tentacles, and in animals with unilateral lesions of the posterior tentacles. Tentacular function was evaluated under three different conditions. 2. One assay required the snails to locomote upwind in a two-armed olfactometer and enter the side in which the airstream contained a food odor. The performance of intact controls was statistically indistinguishable from that of snails with bilateral anterior tentacle lesions or snails with unilateral lesions of the posterior tentacles. Snails lacking both posterior tentacles performed at chance levels (Table 1). 3. The second assay consisted of trail following on a mucus slime trail. Bilateral posterior tentacle amputations were without effect, but bilateral amputations of the anterior tentacles led to a significant deficit compared to intact controls (Table 2). 4. The third assay measured the accuracy of locomotion to a distant odor source in still air. A circular arena was employed. Intact snails and snails with bilateral lesions of the anterior tentacles consistently oriented with a high degree of accuracy. Animals with unilateral or bilateral lesions of the posterior tentacles failed to orient. The unilateral amputations produced a turning bias towards the intact side (Fig. 2). 5. The results demonstrate thatAchatina can orient to olfactory stimuli by at least three different means, namely, anemotaxis, movement up a concentration gradient and trail following. The anterior and posterior tentacles are involved differentially in these behaviors. Also, anemotaxis requires only a single tentacle (klinotaxis), whereas orientation to concentration gradients utilizes simultaneous bilateral comparisons (tropotaxis) (Table 3).