In total, 308 paired-samples of teat duct material and milk, were collected before and 50-70 min after machine-milking, from 30 ewes. Samples were processed bacteriologically. For analysis of results, we compared changes in bacterial isolation following milking, for duct and milk samples; statistical significance was assessed by the Sign Test. Bacteria were isolated from 18 (6%) duct and 19 (6%) milk samples collected before the milking procedure; respective figures after it, were 81 (26%) and 33 (11%). In 77 (25%) cases, bacteriological findings in the two duct samples of each pair were different; in seven cases bacteria were isolated only before, whilst in 70 cases bacteria were isolated only after milking (P < 0.005); respective results for milk samples were 26 (8%): 6 and 20 cases (P = 0.693). The majority of bacterial isolates were staphylococci, accounting for 63% of 99 isolates. The milking procedure predisposes to entrance of bacteria into the teat duct; however, increased bacterial isolation from the teat did not result to increased mammary infections, likely as a consequence of defence mechanisms present in healthy teats.