A quick and simple technique has been developed that is suitable to quantify the concentration of most types of biosurfactants in a typical growth medium using infrared spectroscopy. The area of the peak due to the carbonyl bond of the biosurfactant was measured and compared to the area of the nitrile peak in an internal standard (anthracenecarbonitrile). This ratio showed a linear trend with the concentration of biosurfactant in the medium for concentrations from 0.2 to 3.2 g biosurfactant l(-1). The presence of hydrocarbons in the media and variations in the pH of the media did not interfere with the measurements.