Behavioral responses to homogenates of food and non-food plants are tested in 6 species of Florida Ascoglossa (= Sacoglossa) (Mollusca: Opisthobranchia): Oxynoe azuropunctata Jensen, Elysia evelinae Marcus, E. papillosa Verrill, E. subornata Verrill (= E cauze Marcus), E. tuca Marcus & Marcus, and Ercolania fuscata (Gould). All species show positive responses to homogenates of their usual food plants. The species having the broadest food spectra also show positive responses to the widest array of homogenates. The position of Caulerpa spp. (Chlorophyta: Caulerpales) as the “ancestral” ascoglossan food is reflected by the positive response of almost all ascoglossans tested to at least one specics of Caulerpa, whether or not their diets include Caulerpa spp. For species with relatively broad food spectra the responses to preferred foods are significantly more positive than the responses to less-preferred foods and non-utilized plants. No correlation exists between positive responses and protein level of plant homogenates. After gel-filtration into a fraction containing molecules heavier than approx. 3 500 daltons and a fraction containing molecules lighter than this, the plant homogenates do not elicit statistically significant responses.