Rats were injected with 15 mg/kg (i.p.) mianserin or vehicle (saline) for 4, 10 or 21 days and 5-HT2 receptor binding and mRNA levels measured. Treatment with mianserin induced a substantial decrease in 5-HT2 radioligand binding (44-59% decrease; P less than 0.05 vs. control). No changes in the amount of 5-HT2 or, as a control, beta-actin mRNAs were found (P greater than 0.05 vs. control). These results indicate that mianserin decreases 5-HT2 radioligand binding without altering steady-state 5-HT2 mRNA levels.