Chronic periapical lesions were recognized clinically and radiologically in 109 patients aged from 10 to 79, twice as frequent in the maxilla as in the mandible. Histopathological analysis revealed periapical granulomas and cysts. Forty-eight periapical granulomas were studied histobacteriologically. Detailed microscopic analysis of these cases in order to find bacteria was negative. Histopathological analysis of 72 periapical granulomas and 13 cysts (including four follicular cysts) revealed mixed forms apart from homogenous granulomas. In addition changes in the composition of infiltrate cells are rather qualitative than quantitative, therefore classification of periapical lesions into periapical granulomas and cysts seems justified and sufficient for diagnostic and clinical needs. Detailed analysis of cellular composition of periapical granulomas and cysts shows that immunologic agents may play a role in the pathomechanism of these lesions.