Pretreatment with small doses of fentanyl (100 micrograms) or alfentanil (300 micrograms) was found significantly to reduce the induction dose of thiopentone. Fentanyl 50 micrograms and alfentanil 150 micrograms also significantly reduced the onset time and increased the consistency of action of midazolam. Respiratory depression was not a problem when 50 micrograms fentanyl or 150 micrograms alfentanil were used.