Two cases of contact allergy to methylisothiazolinones from slimicides used in pulp and paper mills are described. The first patient worked as a batcher in a paper mill, and he was in charge of pumping slimicides containing methylisothiazolinones. During pumping, the liquid often overflowed, and his clothes were wet daily with slimicides. After 3 months of work, he began to suffer from dermatitis, which improved when he was away from work. A clinical investigation confirmed the dermatitis diagnosis and a positive skin patch test to Kathon CG was found. The second patient worked as an agent for a firm marketing slimicides containing methylisothiazolinones. One of his tasks was to pump slimicides into the mills, and during such operations his clothes often got wet from slimicides. After some years of work, he began to suffer from erythema and dermatitis after contact with the slimicides. A skin patch test showed a strongly positive reaction to Kathon CG. These case reports draw the attention to the fact that employees in the pulp and paper industry handling slimicides are exposed to extraordinarily high concentrations of methylisothiazolinones and run a substantial risk of being sensitized. The report also stresses the need for improved handling routines of those strong sensitizers in the paper mills.