101 samples of faeces, colonic mucosa and rectal swabs taken from 100 pigs (29 commercial herds) were cultivated on Trypticase Soy Agar with 5% of sheep blood, spectinomycin (200 mg/l), vancomycin (50 mg/l), rifampicin (12.5 mg/l) and colistin (12.5 mg/l). Plates were incubated in an anaerobic container at 37°C for 5–7 days. 25 samples (10 faeces, 15 scrapings of colonic mucosa) were examined by darkfield microscopy for the presence of spirochaetes. In 80 samples (21 faeces, 31 rectal swabs, 28 scrapings of colonic mucosa) from diarrhoeic pigs 44 isolates of spirochaetes were identified by PCR method as Brachyspira hyodysenteriae. In 21 samples (20 rectal swabs, 1 scraping of colonic mucosa) taken from apparently healthy pigs in herds with swine dysentery were isolated weakly haemolytic spirochaetes: B. intermedia in 5 samples and phenotypic group III brachyspirae in 4 samples. Minimal inhibitory concentration (MIC) of tylosin, tiamulin and valnemulin was determined by the agar dilution method. To tylosin 16 out of 17 strains of B. hyodysenteriae were resistant (MIC 64 and 256 µg/l), one strain was susceptible (MIC l µg/ml). To tiamulin 17 out of 19 strains were susceptible (MIC from 0.016 to 0.25 µg/ml), one strain was intermediately susceptible (MIC 2 µg/ml) and one resistant (MIC 32 µg/ml). To valnemulin 17 out of 19 strains were susceptible (MIC from 0.016 to 0.064 µg/ml), one strain was intermediately susceptible (MIC2µg/ml) and one was resistant (MIC 8 µg/ml). Valnemulin resistant strain was also resistant to tiamulin.