Measurements were made to determine the effect of air-flow on the sensitivity of microphone phobes. Standard condenser microphones fitted with either a standard nose cone or a slit-tube were investigated. A slit-tube is a special device to suppress the turbulent noise signal when sound measurements are to be made within a flow. The experiments show that there is a loss of the acoustic sensitivity due to the air-flow. However, the mean sensitivity loss is less than 0·5 dB up to 40 m/s and within a frequency range from 40 Hz to 1250 Hz. Therefore the loss in sensitivity may be neglected for most practical measurements.