Responses tested in individually caged, fifth-instar nymphs of the potato leafhopper, Empoasca fabae (Harris), included the rate of initial imbibition (by a colorscoring method) and survival (leafhopper survival hours, LSH) within 72-hr exposure in darkness, at 29°C, to a histidine-buffered, rhodamine-B-dyed agar substrate containing the test compound, or sucrose, or both. Tomatine elicited the most sharply defined reactions. Measured by rate of initial imbibition, the leafhopper sensitivity threshold to this compound was slightly higher than 1×10−1M; tomatine at 1×10−2M completely restricted imbibition; and the rate of nymphal mortality increased with increase in tomatine concentration. Tomatidine did not affect either the rate of imbibition or the LSH. Solanine, solanidine, and demissidine reduced the rate of initial imbibition, but not the LSH, while leptine I, extracted from the leaves of Solanum chacoense, markedly reduced both the imbibition rate and the LSH. When sucrose was added to tests with solanine, solanidine, demissidine, and tomatine, the ensuing imbibition rates were partly dependent upon the sucrose effect. Some of the same components of Solanum plants to which Leptinotarsa decemlineata (Say) has been found responsive are potentially active ecologically in the interactions of these plants and E. fabae.