Lactate concentration, fibrinogen and fibrin(ogen) -- degradation-products in central venous blood were analysed in 35 unconscious patient with acute hypnotic drug poisoning (HDP) and compared with the results in 13 healthy control persons undergoing the same degree of forced diuresis via central venous catheters. Blood samples were taken on admission and at 12 h intervals up to 36 h after admission. Patients with HDP were attributed to the categories of moderate intoxications (n = 17) and severe intoxications (n = 18) according to their clinical condition. On admission, blood lactate was significantly higher in severe intoxication (3.90 +/- 2.94 mmol/l) as compared to the control group (1.25 +/- 0.17 mmol/l). Blood lactate was less elevated in moderate poisoning (2.74 +/- 1.22 mmol/l). Thirty-six hours after admission blood lactate was completely normalised in patients with moderate intoxication (1.19 +/- 0.69 mmol/l) but still significantly elevated in severely poisoned patients (2.26 +/- 1.48 mmol/l). Lactate concentration was above normal in 15 out of 17 patients with moderate and in 17 out of 18 patients with severe poisoning. A statistically significant linear correlation existed between the duration of unconsciousness and the maximal lactate concentration within 12 hrs after admission. For fibrinogen concentrations statistically significant differences were observed neither between groups nor across time. Titers of FDP were elevated in 9 out of 11 patients with moderate and to a higher degree in all patients with severe poisoning, indicating low rate DIC. Hyperlactatemia is a frequent finding in acute hypnotic drug poisoning. Blood lactate estimations may improve the evaluation of the severity of poisoning and the efficacy of therapeutic interventions.