Naive male rats were observed for 10 min in an open field for 5 successive days. For the first 4 flays, i.p. injections were made with either S (saline) or D (chlordiazepoxide at 10, 20 or 40 mg/2 ml/kg) 30 min prior to observation and on the following 2 days, the S rats were treated with either S or D (at one of the 3 doses), while the D rats with either D (at the same dose) or S. The drug-state changes (both from S to D and D to S) increased ambulation and rearing in the open field with D at 10 mg/kg, but at higher doses the same effect was found only from D to S probably because of the drug's stronger muscle relaxant action. The same "dishabituation" effect was observed in terms of defecation and urination with the D-to-S shift but not with the reverse shift probably because of the drug's depressant effect upon defecation and urination; in addition the dose-response relationship failed to appear as in ambulation and rearing. Correlations between the 2 skeletal measures and the 2 autonomic measures were very low.