Measurements of the backfat thickness over the last rib, 65 mm from the dorsal midline, were taken on 122 live pigs with five different ultasonic machines: Sonatest, Medata, Renco, Sonalyser and Ilis. These measurements were examined for their ability to predict the corresponding carcass introscope measurements. Each pig was measured with each machine 6 d before slaughter and carcass measurement. The RSDs for predicting introscope measurements were 2.35 mm (Sonatest), 2.43 mm (Sonalyser), 2.56 mm (Renco), 2.72 mm (Medata) and 2.90 mm (Ilis). The inclusion of liveweight in the prediction equation gave a small but significant improvement in the RSDs of all machines. The results suggest that none of the machines tested could predict backfat thickness satisfactorily for grading of pigs before slaughter.