Fine-structural study of large, vacuole-like structures of the human corticotroph cell (‘enigmatic body’; EB) revealed that these bodies have a preferential juxtanuclear position in the vicinity of the Golgi complex. EBs have rugged outlines, frequently a narrow electron-dense rim and numerous membrane-bound compartments in an almost homogeneous matrix of low electron density. Fusion between EBs and secretory granules and other cytoplasmic components was noted. The peripheral rim and the matrix exhibited moderate to strong acid phosphatase activity. The inner compartments were consistently negative. It is proposed that EBs represent special lysosomes and serve as centers for recycling secretory material, as well as for storage and release of degraded produ