The following frequencies of change between 30 kPa milking vacuum and atmospheric pressure were used in a milking experiment with single-space cups: 0.05 Hz, 0.1 Hz, 0.2 Hz, 0.35 Hz, 0.5 Hz, 0.65 Hz, 0.8 Hz, and 0.95 Hz. Milking cup pressure and instantaneous milk flow rate through the teat canal were repetitively recorded ten times per second. Four clearly distinguishable and reproducible forms of flow rate oscillations were observed across several sucking phases together with four equally distinguishable and reproducible forms of profiles of a variable milk flow rate within one sucking phase. The occurrence of those differentiated forms of milk flow was found to be correlated primarily with both the sucking phase frequency applied and the average milk flow rate. These findings seem to be indicative of active control of teat canal diameter or milk flow rate by the unstriated teat musculature.