Parathyroid hormone-related protein (PTHrP), calcium (Ca), magnesium (Mg), inorganic phosphate (P-i), fat, protein, and lactose concentrations were measured in milk of eight 4-10-year-old Brown Swiss cows during daytime at intervals of about 2 h. A commercial I-125 radio-immunoassay was used to quantify the concentration of PTHrP. A repeated-measurement analysis of variance followed by contrasts revealed changes with time in the concentration of fat, protein, lactose, and P-i. Fat concentration clearly increased, whereas protein concentration slightly decreased after each milking. Lactose concentration slightly decreased after the morning milking and slightly increased just before the evening milking. P-i concentration slightly decreased after the morning milking and between the two samplings after the evening milking. Changes with time were not observed for PTHrP, Ca, and Mg. No associations of changes with time were found between the concentrations of PTHrP and the other measured milk components. Thus, a paracrine/autocrine role of PTHrP in the transport of minerals into bovine milk cannot be demonstrated by this data.