Temperature effects on the mating call of the gray tree frog (H. versicolor) in Missouri [USA] were intensively studied in the field and laboratory. Pulse repetition rate increased and remained linear throughout the 24.3.degree. C temperature range in which the frogs were recorded (from 9.2.degree.-33.5.degree. C), supporting Walker''s (1975) assumptions about the linearity of the temperature dependence of rates within a poikilotherm''s nervous system. Inter-call interval, call duration, pulse duration and pulse number decrease with an associated increase in temperature; dominant frequency increased only slightly.