The incidence of staphylococcal mastitis was investigated in 3 large commercial Friesland herds before and after the single intracisternal administration, during the dry-period, of 1 of 4 formulations containing staphylococcal antigens, antibiotics and base alone or in combination. Results suggest that the instillation of vaccine alone and vaccine plus antibiotics into fully involuted quarters very significantly reduced the incidence of staphylococcal mastitis in the subsequent lactation. Compared with antibiotics and base, each administered alone, the vaccine reduced the number of infected quarters in the subsequent lactation by 70,52% and 79,52% respectively, whereas the corresponding values for vaccine plus antibiotics were 62,22% and 71,22% respectively. The difference in results between vaccine alone and vaccine plus antibiotics is statistically insignificant, as is the difference between the results achieved by antiobiotics and base alone. The vaccine plus antibiotics is thought to possess combined therapeutic-preventive activity. The investigation showed, however, that vaccine plus antibiotics consistently protected mastitis negative quarters against new attacks of staphylococcal mastitis during the subsequent lactation period about 1,43, 4,00 and 5,32 times more effectively than did vaccine, antibiotics and base used individually.