Antiepilepsirine (AES) is one of the derivatives of a Chinese folk prescription. It is a new antiepileptic drug (AED) synthesized in cooperation by Chinese medical and pharmaceutical workers. Pharmacological experiments on animal models prove that its antiepileptic action is marked, but there has been little evaluation of its clinical effects. We used the double-blind placebo-controlled crossover study which is generally acceptable as a proper method for new drug study. This study covered 58 epileptic children treated with classical AEDs and observed 6.5 months. Every patient took AES and placebo for 3 months each by random crossover on the basis of add-on therapy. The blood levels of AES and other antiepileptic drugs were determined regularly. The results show that there are no significant differences in clinical effects between AES and placebo in pediatric epilepsies as a whole, but AES is effective in tonic-clonic seizures (P less than 0.05), the most common type of seizure in the series. There are no significant differences in AED blood levels between the AES effective and ineffective groups. AES has no effect on the blood levels of other AEDs. AES is very safe, children given large doses (10 mg/kg/day) demonstrate no serious side-effects. It is suggested that there is potential improvement in patient psychological and cognitive status. This article also discusses the evaluation of new drugs for clinical effects, subject sampling, the criteria for efficacy evaluation and relationship between animal information and human outcome. The AES chemical structure is different from other well-known AEDs, this is a unique advantage.(ABSTRACT TRUNCATED AT 250 WORDS)