The aim of this study was to analyse the effects of environmental factors on somatic cell count (SCC) and total microorganisms count (TMC) in cow bulk tank milk. The investigations were carried out in 2003 in 200 farms, situated in the Wielkopolska region. In the period from May to September, higher levels of SCC and TMC in milk were observed than in the other months. The average number of cows in the herd was positively correlated (i.e. disadvantageously) with the level of SCC. The following management and technological factors decreased both the level of SCC and TMC: keeping cows without pigs in the same farm, pre-milking udder and teat cleaning with a dry towel, use of antibiotics at cow dry-off, individual registration of the cases of clinical mastitis, antibiotic treatment of all cows with the clinical manifestation of mastitis, and pre-treatment performing of antibiogrammes in mastitic cows. Furthermore, a decreased level of SCC was associated with the following factors: use of cow-runs in the summer season, use of California Mastitis Test, and use of concentrates in the amount greater than 4 kg per cow/day. A decreased level of TMC was observed in the herds in which cow-runs were not used in the winter season, pipe-line system of milking was used, milking cluster was stored between milkings dry or it was dipped in the water containing a disinfectant, disinfection of all stalls for cows was performed at least once per year, and sugar beet leaves were not used in cow feeding.