Tests of drugs Florfenicol 40% LLC «AVZ SP » and Florox LLC «NITA PHARM» from the group of fenicols for bacterial respiratory and intestinal infections were carried out on 43 calves 1.5- 3.5 months old in a large dairy complex in the Central District of the Russian Federation.Based on the results of bacteriological studies before the use of antibiotics Florfenicol 40% and Florox, in lavages from the upper respiratory tract and intestines of calves of experimental and control groups, Corynebacterium spp., Staphylococcus spp., Staphylococcus aureus, Streptococcus spp., Enterococcus spp., Micrococcus spp., Moraxella bovis, Pseudomonas spp., Proteus spp., Bordetella bronchiseptica, Neisseria spp., Clostridium spp., Escherichia spp., Enterobacter spp., Citrobacter spp., Serratia spp., Edvardsiella spp., Providencia spp., Salmonella spp., including pathogenic serotypes and bacterial strains.The results of bacteriological studies of isolated cultures from calves of experimental and control groups after specific therapy showed the absence of pathogenic serotypes and strains of Escherichia coli, Staphylococcus aureus, Bordetella bronchiseptica, Pseudomonas spp., Salmonella spp. in swabs from the nasal cavity and rectum, but the presence of non-fermentative forms of Escherichia spp. and other opportunistic bacteria.Based on the results obtained, it was found that the drug Florfenicol 40% in doses of 1 ml per 20 kg of body weight intramuscularly twice with an interval of 48 hours and 2 ml per 20 kg subcutaneously once has a pronounced activity against aerobic and facultative anaerobic bacteria. According to the results of hematological and biochemical studies, the antibiotic Florfenicol 40% does not have a negative effect on homeostasis with a positive effect on metabolic processes and a decrease in the activity of acute and chronic inflammation in tissues and organs