The effect of the non-selective treatment of dairy cows with antibiotics (Chronicin foam--Galena, and Masticort PS--Poland) and the effect of teat disinfection (Jodonal A--Lachema) at the last milking in lactation was studied as exerted on the reduction in the occurrence of infection processes in mammary gland after calving. The trials were performed with 180 cows in three groups of 60 animals. At the last milking the mammary secretion of each cow was sampled for bacteriological examination. Two cow groups were treated at the same time. The occurrence of infection processes in the mammary gland in the period after calving can be characterized as follows: a) in the period after calving the control group had an increased proportion of cows with an infection process in their udders (from 58.3% at the end of lactation to 68.3% in the period of 14 days following calving); b) in the group treated with Chronicin foam the infection was reduced by 3/5, i. e. from 71.7% of cows infected at the start of drying off to 28.3% with infection process after calving; c) in the group treated with Masticort PS the infection after calving was reduced by 3/4 as compared with the infection at the onset of drying off, i. e. from 80% to 20%. In the control group 20% of the cows recovered spontaneously. The preparation Chronicin foam showed 79.1% therapeutic effectiveness. Therapy with Masticort PS was successful in 81.3% of the animals.(ABSTRACT TRUNCATED AT 250 WORDS)