The authors have carried out a survey of 23 bacteriology laboratories to investigate tuberculous contaminations which took place from 1967 to 1972 in these laboratories. They have reviewed 20 accidents in 74 technicians who performs searches for tuberculous bacilli, and 29 accidents in the total amount of 379 technicians working in these 23 laboratories. A comparison of these results with the previous published investigations shows a rather high number of cases reported in our country. A review of the possible causes of contaminations leads to suspect bacterial aerosols and to put forward the use of laminar flow enclosures as a prevention. The authors have tested several vertical flow instruments built to different patterns. All three convenient enclosures have an architectural characteristic: their blowing ceiling overhangs the working plane. As these instruments have been under examination for three years in a laboratory where contaminations are very likely to happen, they have obtained interesting results.