SUMMARY Lignocaine is commonly used for local anesthesia during fibreoptic bronchoscopy (FOB). Its toxicity is related to plasma concentrations. Aim of our study was to record the plasma concentrations of lignocaine before, during and after FOB and to evaluate whether the dose for nasal and endobronchial anesthesia has any correlation with the peak serum concentrations of the drug. Twelve patients (mean age 57±3 yr SEM) undergoing FOB were studied. Mean time of FOB was 27 ± 2min. None of our patients had a history of cardiac disease, was on any regular medication neither suffered from hepatic or renal failure. Lignocaine was administered as 2% solution using a larynx-syringe (mean dose 100 mg), 2% gel (mean dose 182.5±15mg) and finally 2% solution through the bronchoscope (mean dose 339±12 mg). Total dose was within 500-720mg (622±20mg). Venous blood samples were drawn before the beginning of local anesthesia and then at time 5, 10, 20, 60, 90 and 120 min after that. ECG, blood pressure and oxygen saturation were simultaneously recorded. Our results showed that peak plasma concentrations of lignocaine in 8 patients were reached within 20 min (2.15±0.4 μg/ml), in 3 patients within 30 min (1.9±0.3 μg/ml) and in one patient within 60 min from the beginning of local anesthesia (1.81 μg/ml). None of our patients exceeded the critical level of toxicity (5 μg/ml). Two hours after the beginning of local anesthesia lignocaine's concentrations were still measured (1.48±0.15 μg/ml). There was a significant positive correlation between total dose of lignocaine and peak serum concentration (r=0.63, p, 0.05). Similar correlation was found between endobronchial dose of lignocaine and peak serum concentration (r=0.64 p=0.02). No correlation was found between dose for nasal anesthesia and peak serum concentration of the drug. No adverse reactions were observed. In conclusion, local administration of lignocaine during FOB usually exceeds the proposed highest dose (400mg), but even in this occasion, drug administration is usually safe with no toxic levels observed. Peak plasma concentrations were found within 20-30 min from the beginning of local anesthesia. Dose for nasal anesthesia expresses a significant percentage of the total dose but with no correlation with peak serum concentration. Pneumon 1999, 12 (1): 32-38