Clinical pharmacology of pipecuronium; a comparative study of its duration of action between balanced (propofol/fentanyl) and isoflurane anesthesia. Pipecuronium duration of action has been compared between patients under balanced (propofol/fentanyl) or 0.8-1 Mac isoflurane anesthesia. T1/TC 10-25-50-75-90% (T1/TC, 10, T1/TC, 25, T1/TC, 50 TOF, 75T1/TC 90) and TOF 10-25-50-75% (TOF 10%, TOF 25%, TOF 50%, TOF 75%) ratios were studied; T1/TC 10-75% (T1/TC 10/75) and TOF 10-75% (TOF 10-75%) recovery times were also derived. The muscle relaxant has been utilized in 55 patients divided into groups according to the method of its administration: in group I (33 patients) the drug was injected in small divided doses until ED95% was reached, according to the cumulative dosage method; in group II (8 patients) and III (12) the drug was injected at 0.35 micrograms/kg and 50 micrograms/kg respectively. Neuromuscular function was monitored by isometric force transduction, stimulating the adductor pollicis by tof every 12 sec. Pipecuronium duration of action (min) following single doses was longer than following the cumulative dosage method (TOF 25% vs 61%, TOF 50% 103 vs 76, TOF 75% 136 vs 102). The presence of isoflurane significantly prolonged recovery times (TOF 10%, from 55 to 70, TOF 25% from 61 to 88, TOF 50% from 75 to 120) in group I (cumulative doses) patients. Recovery times were dose related, while age did influence recovery only at the earlier intervals (T1/TC 10 and 25%). Keeping in mind the limited range of age and dosages, advantages and disadvantages of the drug are discussed, comparing the experimental results with those derived from the literature.