A method for controlling operation of a CPAP apparatus. The apparatus has a blower (2), a patient interface (6), an air delivery conduit (8) for delivering air from the blower (2) to the patient interface (6), a sensor (4p) for determining the pressure in the patient interface (6), and a control mechanism (15) that causes air to be delivered at a desired pressure to the patient interface (6) and that detects transitions between inhalation and exhalation of a respiratory cycle of a patient in order to synchronise the blower output with the patient's efforts. In one form the CPAP apparatus provides pressure in accordance with a bi-level waveform with at least one characterising parameter of the waveform being automatically adjusted in accordance with indications of sleep disordered breathing. The indications of sleep disordered breathing can be one or more of snoring, apnea, hypopnea, and flow limitation.