The authors describe the case of a 22-year-old woman treated with doxycycline on account of erythema on the buttock which developed after a sting by a tick and was evaluated as erythema chronicum migrans. In the course of three-week treatment with doxycycline, at the seaside a phototoxic reaction developed - erythema on uncovered parts of the body, and one week after termination of treatment pain developed associated with onycholysis of the proximal parts of the nails of all fingers on both hands with maximum affection of the thumb.

        Key words: photoonycholysis - antibiotic treatment - doxycycline