A survey was performed during Oct., 1976 to May, 1977 in which the milking plants on 328 Norwegian dairy farms were tested according to Norwegian recommendations and to the more detailed prescriptions for tests and assessment. Only plants in herds housed in cowsheds were included, the mean herd size being 19 cows. The herds were selected at random from those supporting the milk recording scheme. Approximately 14% were bucket plants, the remainder being pipeline plants. The mean age of the plant was approximately 5 yr. Approximately 14% of the vacuum pumps had insufficient capacity. The vacuum regulators were installed in an unacceptable place in 9.1% of the plants; the vacuum level was too high in 3.7%. Other tests on the regulators (regulation area, slowness and stability) showed poor standards in 4-8% of the plants. The diameter of the different sections of the air pipeline was unacceptable in 27.1% (main air pipeline), 31.1% (tap line trunk) and 9.8% (tap line) of the plants. The leakage of air into the air pipeline was too high in 51.7% of the cases. The diameter of the milk pipeline was unacceptable in 32.4% and air leakage too high in 51.8% of the plants. These pipeline faults occurred more frequently in older plants than in plants of more recent installation. The degree of undulation of the milk pipeline was assessed as poor in 20.4% of the pipeline plants. Concerning the pulsators, these were poor with regard to rate in 12.1% of cases and with regard to the limping ratio in 6.3%. Recordings of 19 different properties in the case of pipeline plants and 15 for bucket plants were assessed as major faults if they did not fulfil the recommendations defined. The distribution of these faults was studied in relation to manufacturer and the age of the plant. Considerable differences for some of the properties were found between the geographical areas where the plants were located. Altogether, the frequency of milking machine faults support the need for regular test and service programs.