Tremor induced by TRH and oxotremorine was recorded by a capacitance transducer, and its intensity and frequency were evaluated using power arrays. In mice treated with TRH (20 mg/kg, i.p.), the latency of tremor was 17.1 +/- 1.7 min (mean +/- S.E.) and the duration was 20.4 +/- 2.2 min, while the frequency was 13.7 +/- 0.3 Hz. In animals with oxotremorine (0.5 mg/kg, i.p.), the latency was 4.3 +/- 0.4 min and the duration was 18 +/- 2.2 min, while the frequency was 12.7 +/- 0.3 Hz. The latter frequency, however, was significantly shifted to a lower frequency as a function of time. In TRH-induced tremor, vertical movements appeared in the same degree as horizontal movements. In oxotremorine-induced tremor, the vertical movements were few, whereas the horizontal movements were observed in a degree similar to those of TRH. The TRH tremor was suppressed by haloperidol and propranolol, but not by atropine. On the contrary, the oxotremorine tremor was inhibited by atropine, but not by haloperidol or propranolol. These results suggest that mechanisms of tremor induced by TRH differ qualitatively from those by oxotremorine; dopaminergic and beta-adrenergic receptor mediated functions may be linked to the developments of tremor caused by TRH, while cholinergic systems have a little effect in mice. The apparatus used in this study and power spectral analysis with power arrays may provide a useful method for simultaneous evaluation of the latency, duration, intensity and frequency of tremors.