Chronic treatment (2 weeks) with piracetam (500 mg/kg, once daily PO) elevated m-cholinoceptor density in the frontal cortex of aged (18 months) female mice by about 30-40%, but had no effect on m-cholinoceptor density in the frontal cortex of young (4 weeks) mice. The effect of piracetam on m-cholinoceptor density as determined by the specific binding of tritiated QNB was not affected by concomitant daily treatment with either choline (200 mg/kg) or scopolamine (4 mg/kg). It is concluded that the effect of piracetam on m-cholinoceptor density could explain the positive effects which have been reported for combinations of cholinergic precursor treatment with piracetam on memory and other cognitive functions in aged experimental animals and patients and could also represent part of the possible mechanism of action of piracetam alone.