To examine the relationship between HMGB1 and pulmonary hypertension, we investigated the patterns and levels of HMGB1 expression in lung tissues at 28 days and measured serum levels of HMGB1 at 0, 1, 3, 7, 14, 21, and 28 days after inducing pulmonary hypertension by MCT. The gene discussed is HMGB1; the disease is pulmonary arterial hypertension.