The acceptability by and suitability for larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say), of 104 plant species belonging to 87 genera and 39 families was investigated. Of these 104 species, 36 were accepted to some degree, but only 15 supported growth of fourth-instar larvae to pupation. The 15 plants belong to 5 unrelated families. In addition to the Solanaceae, 4 nonsolanaceous plants supported growth from egg to adult: Asclepias syrioca, A. tuberosa, Capsella bursapastoris, and Lactuca sativa var. romana. A. syriaca and L. s. romana were the most suitable and permitted continuous culturing for several generations. Preference experiments showed discrimination between solanaceous and nonsolanaceous plants. In the presence of potato leaves, the non-host plants were not selected, although in confinement some were accepted and supported growth. This fact suggests that botanically restricted chemicals are of importance. Oviposition preference experiments were conducted to determine the preference of the adults for potato and other plants. Eleven solanaceous and 6 nonsolanaceous plants were tested. In all but 2 cases the potato plant was preferred, the exceptions being Solanum rostratum and S. nigrum. The beetle's strongly positive response to S. nigrum, which is not eaten by cither adults or larvae, proved that oviposition preference of the adult is not a consequence of feeding preference. Capsicum annuum did not elicit oviposition, indicating the presence of inhibitors. It is evident that specific stimuli also are required to induce normal oviposition.