We experienced 4 cases of acute retinal necrosis syndrome, and performed anterior chamber paracentesis as a diagnostic aid in their acute and convalescent phases. The aqueous humor obtained by it was used for measuring antibody titers to herpes group virus and electron microscopic observation. One case showed elevated titer to herpes simplex virus type 1 in the convalescent phase, while the other to varicella-zoster virus, suggesting that these 2 viruses could cause this disease. Electron microscopy showed persistent lymphocytes and macrophages throughout the course, while plasma cells appeared at the height of the inflammation corresponding to the locally elevated antibody titers. There was no electron microscopic evidence of viral infection in the aqueous cells examined.