Trends of certain mastitis markers were studied in udder quarters (n = 201) showing clinical symptoms of acute mastitis. Besides the clinical examination, before the first treatment (baseline sample), and about 3 weeks later, 17 to 24 days following the last treatment (control sample) milk samples were collected for bacteriological identification of the mastitis pathogens and for the determination of certain inflammatory markers: somatic cell count (SCC), N-acetyl-beta-D-glucosaminidase (NAGase) and alpha 1-antitrypsin (ATR) activities, as well as bovine serum albumin (BSA) and chloride (Cl-) concentrations. Based upon the clinical and bacteriological status as well as the SCC recorded at the control investigations, 6 groups were established (recovered, latently infected, subclinical mastitis: bacteriologically positive and negative, as well as clinical mastitis: bacteriologically positive and negative). As compared to the baseline samples, all parameters decreased in the case of recovered udder quarters, as well as in those with abated latent infection or subclinical mastitis at the time of control examination. Comparing the control samples of the different categories, characteristic differences were found in NAGase activity, indicating the grade of cytodamaging effect of mastitis. Of the other markers, ATR and Cl- proved to be more adequate for the differentiation than BSA. It can be concluded that, in addition to SCC, first of all NAGase can be recommended for use as an inflammatory parameter in pharmacodynamic studies. Besides these two parameters, ATR and Cl- can also be chosen as a possible third marker.