Simulators may be used in training personnel for the situations when consequences of inappropriate action could be dangerous or expensive. Mishaps and accidents in connection with the use of biomedical instrumentation are frequently a result of technical malfunction and improper use of the equipment. In the medical field, however, use of simulators is not very common. This paper reports our experiences of a development project to design the "PatSim' hands-on simulator for training anaesthesia and intensive care personnel. The simulator consists of a manikin positioned on an operation table or in a typical critical care bed. The manikin, which is controlled by a standard personal computer (PC), can be ventilated by an anaesthesia machine or a ventilator, intravenous pumps can also be connected. Any standard electrodes and transducers can be used to pick up parameters, like ECG, invasive and non-invasive blood pressure, airway pressure and CO2. Data can be displayed on any monitor or workstation. There is no need for modification or special adaptation of the medical equipment used in the simulation scenario. The manikin is capable of spontaneous breathing. Controlled from the PC, different clinical signs can be developed. In addition, typical clinical symptoms can be created during the simulated treatment period. They include laryngospasm, change of lung compliance or airway resistance, pneumothorax, leakage of the intubation tube cuff, blocking of the breathing sounds from one lung, secretion, gastric regurgitation and diuresis. During a simulation session, the trainee should be exposed to a lifelike situation. Hence, we place the manikin in a room that resembles either intensive care or operating room environment.