The effects of inhibition of nitric oxide (NO) or serotonin (injection of nitro-L-arginine methyl ester (L-NAME) or 5,6-dihydroxytryptamine (5,6-DHT), respectively) on food-attraction conditioning was investigated in Helix. Blocking NO synthase (NOS) prior to conditioning significantly impaired the food-finding ability of the snails. Food-conditioned snails, after inhibition of NOS, remained able to locate the conditioned food. These results indicate that the acquisition of memory depends on NO, whereas memory recall and olfactory orientation are not dependent. Ablating the serotonergic system did not influence food-attraction conditioning, suggesting that food-attraction conditioning may be at variance with conventional associative conditioning procedures.