Twenty infants aged 1-2 years who had previously had one attack of febrile convulsions were randomly given a single dose of diazepam rectally, either as a solution (0.7 mg/kg) or by suppository (5 mg). Plasma-diazepam levels were determined repeatedly during the first hour using gas chromatography. Rectal administration of diazepam in solution resulted in anticonvulsant plasma values within 4 +/- 1 min. Similar plasma levels were obtained only after 20-30 min in the group treated with suppositories. Diazepam in solution given rectally may therefore be useful in the acute treatment of febrile convulsions, while treatment by suppository would seem to be of little value in this respect. Moreover, diazepam in solution given rectally seems suitable for use at home in case of recurrent febrile convulsions. This treatment, however, cannot be recommended until the anticonvulsant effect and side-effects have been elucidated further.