Calcific eggs of Schistosoma haematobium were separated from an inactive sandy patch in a cystectomy specimen from an Egyptian farmer; the purified egg suspension was injected into tail veins of inbred mice, some of which were killed immediately and some at intervals of 1, 2, 11, 14, 30, 90, 120, 180, and 365 days. Lungs were examined by tissue digestion and histologic analysis. Calific egg burdens decayed in an exponential manner (eggs/g of lung tissue = 284.9e-0.001x where e = natural log and x = time in days), with a loss of 5,610 eggs/g of lung tissue, i.e., 98% reduction over the year of the experiment. Histologic examination revealed that calcific S. haematobium eggs incited a typical granulomatous reaction as they decalcified. Compared with viable egg granulomata, the response to calcific eggs was accelerated in onset, of lesser magnitude but persisted longer. Small numbers of calcific eggs persisted for at least 1 year after injection of either viable or calcific eggs. It is concluded that despite the apparent lack of tissue reaction to calcific eggs in chronic bladder lesions, these eggs are not antigenically exhausted foreign bodies. Moreover, it is shown that calcific eggs are degraded in significant numbers by mammalian tissue.