Abstract: A respiration test method for providing accurate test signals which may be sed to measure the duration of a subject's inhalation and exhalation periods, and electronic timing circuits for performing such methods. The circuit includes a clock and two flow detectors. One flow detector senses inhalation while the other senses exhalation of a subject. A logic circuit selectively transmits clock pulses from the clock to an inspiratory clock output and an expiratory clock output. The flow detectors generate two-state inhalation and exhalation signals that are at a first state during the duration of the respective inhalation and exhalation periods plus a small timing-out period. The logic circuit, which is connected to clock and the flow detectors, transmits the clock pulses from the clock to the inspiratory clock output when the inhalation signal is at the first state, and to the expiratory clock output when the exhalation signal is at the first state.