1. Case reports are presented of 5 cases of acute infectious lymphocytosis in siblings, ages 2¼-10 years. Symptoms included diarrhea, abdominal pain, vomiting, fever and cough. There was an absolute lymphocytosis lasting about three weeks. All of the cases had elevated eosinophil counts during the course of the disease. Four of the 5 had an eosinophilia lasting several months.
2. The clinical features are reviewed.
3. The morphology of the lymphocytes is discussed in detail.