To study the effect of chronically infected sites on the immediate placement of implants, periapical lesions were induced in the third and fourth premolars of four dogs and the contralateral teeth were used as controls. Nine months after the induction of periapical lesions, experimental and control teeth were extracted, and 28 IMZ implants were immediately placed. After a healing period of 12 weeks, the animals were sacrificed, the hemimandibles were removed, and specimens were prepared to be hard-sectioned and stained with toluidine blue. All areas healed without inflammation or exudation and all implants were clinically immobile and were radiographically determined to be surrounded by normal-appearing bone. Histologically, there were no signs of infection, and the histomorphometric analyses revealed that 28.6% and 38.7% had osseointegrated for the experimental and control implants, respectively. The difference was not statistically significant. It was concluded that chronically infected sites, such as those showing signs of periapical pathosis, may not be a contraindication for immediate implants, if certain clinical measures and preoperative and postoperative care are taken. Schlagwörter: immediate implants, implants, IMZ, infected site, osseointegration