A procedure is described to calibrate XBT probes at one temperature point immediately before launching. The individual XBT temperature offsets are determined by using a stirred calibration bath and a stable, accurate reference thermometer designed for field use. The proposed calibration procedure increases XBT temperature accuracy considerably, while it hardly raises time and effort spent on standard XBT drops. The performance of the system in the field and in the laboratory is described. It is shown that the achieved temperature accuracy is about 0.03 K, and is basically limited by the used reference thermometer. © 1993.