The construction of the Channel Tunnel is one of the largest civil engineering projects ever undertaken. The British drive employed 5900 underground workers, and a number developed dermatitis during 1990/1991. As a result, the Translink Joint Venture (TLJV) Medical Centre set up a surveillance programme aiming to monitor and investigate the men working closely with cement as well as other groups of workers with skin problems. Men attended the Medical Centre voluntarily and were assessed, including history, examination and patch tests to a series of 15 test substances (from the European standard series) where indicated. A programme of education about the hazards of working with cement was instituted, including leaflets, videos, local newspaper articles and personal explanation by the Medical Centre staff. Between January 1990 and January 1992, 1138 men were seen at the Medical Centre regarding their skin and 332 were diagnosed as having occupational dermatitis, past or present. Patch tests were performed on 180 men from all trades. Of the 800 grouters, 466 (58 per cent) were assessed and 111 had a history of occupational dermatitis at some time. Many gave a history of a single episode of dermatitis during a particularly hot and wet phase of tunnelling. Patch tests performed on 86 grouters showed allergy to chromate in 56 (65 per cent). Of the 466 grouters assessed, 17 per cent had positive patch tests to chromate but men with no skin problems past or present were not patch tested. Cobalt allergy was often found with chromate allergy (50 out of 56).(ABSTRACT TRUNCATED AT 250 WORDS)