Over a short period of time, there was an outbreak of work-related skin lesions among workers at a company producing flooring laminate boards, after the introduction of a water-repellent lacquer based on diphenylmethane-4,4'-diisocyanate (MDI). In 5 workers, patch testing was performed with a standard series, an isocyanate series and work-environmental products when indicated. 3 of the workers were tested with the lacquer, and contact allergy was found with concurrent reactions to 4,4'-diaminodiphenylmethane (MDA). 1 of the 3 workers also showed a simultaneous reaction to MDI, whereas 1 showed a positive reaction to dicyclohexylmethane-4,4'-diisocyanate (HMDI). Of the 2 individuals not tested with the lacquer, 1 reacted to both MDI and MDA, whereas the other reacted to a soap used at work. In 3 of 4 cases, the isocyanate reactions appeared after D3. Occupational contact with isocyanates should not exclusively be focused upon respiratory hazards, as this report shows that skin contamination probably increases the risk of developing contact allergy to isocyanates and isocyanate-related substances. When aiming at diagnosing contact allergy to isocyanates, it is desirable to perform a late reading, as positive reactions appear late. MDA appears to be a good marker for isocyanate hypersensitivity.