In the summer of 2001 the obligate, intermittent tropical rat mite Ornithonyssus bacoti attacked humans in an Icelandic household where infected Mongolian gerbils (Meriones unguiculatus), bought in a local pet shop, had been kept for few months. After a rapid proliferation the mite started attacking the humans living in the house. A boy sharing room with the pets suffered from extensive dermatitis. Optimal conditions for O. bacoti are at 24-26 degrees C and a relative humidity of 47%. Similar conditions frequently occur indoors in Icelandic premises. Therefore, if O. bacoti has been noticed indoors, necessary measures should be undertaken to immediately eliminate the pest.