A statistical study of errors associated with the bathythermograph (BT) has been made from data obtained during eight 3-week cruises to ocean weather stations (OWS) DELTA and ECHO. Simultaneous observations using reversing thermometers, bucket thermometers, and injection thermometers and nine sets of observations using two connected BT's were analyzed. BT instrument bias varies with depth as much as 1F with maximum error occurring in the thermocline. One pair of BT's recorded standard errors that varied from 0.20 to 0.61F with depth and averaged 0.34F. Mean differences between reversing thermometer reference temperatures and BT, bucket, and injection thermometer temperatures were computed. Comparison of these differences indicate that ship injection thermometers averaged 1F high; the BT's and bucket thermometers recorded sea surface temperature with approximately the same degree of accuracy, averaging within 0.5F of the reference temperature. At present, BT observations are processed by the National Oceanographic Data Center without correcting for instrument bias. Comparisons between uncorrected data and data containing a temperature correction factor (TCS) based on bucket thermometer readings indicate that the correction factor increases the average accuracy of the observation; however, the increase in accuracy is small. Accuracy of several examples was decreased by correction. (Author).