The effect of patch testing with modified rosin (1065312) and their components on the diagnosis of contact allergy was examined. Maleopimaric-acid (510394) (MPA) and glyceryl-1-monoabietate (GMA) were clinically tested in patients in Stockholm. In Lisbon, Portuguese gum-rosin, formaldehyde modified gum-rosin, fumaric-acid modified gum-rosin, and fumaric-acid and glycerol modified gum-rosin were tested in 665 patients. In addition, MPA was tested in 437 patients. MPA was also tested in seven specialized clinics throughout Europe. Rosin components were analyzed via gas chromatography and high performance liquid chromatography. Of the patients tested in Stockholm, 0.5% to 5.9% reacted positively to 1.2% MPA in petroleum, while 0% to 3.7% reacted positively to the 0.6% MPA in petroleum. Overall, 25 of the 1,072 patients tested reacted positively to 1.2% MPA, 17 of whom did not react to the unmodified rosin. Of the ten patients that reacted positively to GMA, five were negative to the unmodified rosin. In Lisbon, nine of the 655 patients reacted positively to formaldehyde modified gum-rosin and Portuguese gum-rosin, of whom eight also reacted to unmodified gum-rosin. Among the 317 patients tested at a Danish clinic, only one definite reaction to 0.6% MPA was observed. This patient tested negative to the unmodified gum-rosin. At a Belgian clinic, two patients reacted to MPA, one of whom also reacted to the unmodified gum-rosin. The proportions of positive responses to the unmodified gum-rosin at the Danish and Stockholm clinics, up to 6.9% and 5.5%, respectively, were significantly higher than that at the Portugal clinic, up to 1.4%. The authors conclude that patch tests with modified rosins and rosin components should be conducted in patients with unresolved dermatitis, especially when possible exposure to paper, glue, adhesives, or printing inks has occurred.