The aim of this study was to establish a simple and safe method of anaesthesia for intravital microcirculatory observations in small laboratory animals. The usefulness of isoflurane inhalation anaesthesia has been investigated in different strains of mice commonly used in experimental medicine. These were the hairless (hr/hr, n = 12), the BALB/c (n = 12) and the nude mouse (nu/nu, n = 3). Anaesthesia was maintained by mask inhalation of isoflurane vaporized at concentrations of up to 4% in the induction phase, at 1.5% during acute surgical procedures and at 0.8-1.3% during prolonged experimental observations. Isoflurane was vapoured in a N(2)O/O(2) mixture and saturated with 32-36% F(i)O(2). During observations the body temperature was kept constant at 37 degrees C. The tail artery was cannulated for monitoring of mean arterial blood pressure (MAP) and heart rate (HR). To maintain the body fluid balance, isotonic saline was administered at a constant rate of 0.2 ml/h. Arterial blood samples were drawn for blood-gas analysis at the end of the experiments. All animals survived the anaesthesia protocol lasting between 3 and 6.5 h. During isoflurane inhalation, no breathing complications or changes in systemic circulatory parameters were observed. Mean values of MAP and HR were 79+/- 3 mmHg and 486+/- 13 min(-1), respectively, over the entire observation period. A moderate acidosis was recorded in animals under isoflurane anaesthesia, with alterations of arterial blood pH, p(a)O(2) and pCO(2) values (7.29+/- 0.06, 130+/- 19 mmHg and 35.6+/- 4.7 mmHg, respectively). In conclusion, inhalation anaesthesia with isoflurane is useful for experimental studies in the mouse due to (1) the simplicity of administration of the anaesthetic, (2) the rapid induction of anaesthesia, (3) easy control of the depth of anaesthesia, (4) the low percentage of complications, and (5) stable MAP and HR during observations lasting several hours. The proposed technique is especially suitable for observations of the microcirculation under intravital fluorescence microscopy.