Single unit recordings were taken from neurons in the geniculate ganglion of the anesthetized cat. Three groups of chemoresponsive tongue units were identified on the basis of spontaneous activity measures and response to chemical and electrical stimulation of the tongue. Electrical stimulation of the sites of excised fungiform papillae to which tongue units project elicited spikes with latencies of 7–9 msec from group I units, 10–13 msec from group II units and 14 msec or greater from group III units, with little overlap among the groups. The intact tongue was stimulated with different chemical substances. Group I units were preferentially discharged by certain substances such as citric and malic acid, group II units by cysteine and proline. Group III units were affected by fewer substances although some group III units were among those maximally sensitive to mononucleotide salts. Spontaneous activity measures were also utilized to classify the 3 groups, at least in part. The units in the 3 groups innervated fungiform papillae located in different but overlapping regions of the tongue.