Infectious complications are one of the main causes of the lower efficiency of chemotherapy in hematologic oncology. The common infectious pathogens are herpes group viruses. The manifestations of herpesvirus infection or reactivation may be extremely diverse; just the same, digestive tract injury is rarely associated with herpesvirus infection in clinical practice. Viral mucosal injury of the intestine and pharynx is described in 2 patients with lymphomas during agranulocytosis. Virus-specific DNA was absent in blood; however, it was detected at high titers (the number of copies of 103-105 genome-equivalent/ml) in feces and mucosal biopsy specimens. Addition of antiviral therapy could rapidly abolish infectious complications in both cases. Virological examination of material from the injury focus makes it possible to reveal a pathogenic virus even though the latter is undetectable in blood.