A role for inflammation in modulating the extent of angiogenesis has been shown for many organs. The present study was undertaken to evaluate the importance of leukocyte sub-populations for systemic angiogenesis of the lung after left pulmonary artery ligation (LPAL) in a mouse model of chronic pulmonary thromboembolism. Since we previously showed that depletion of neutrophils did not alter the angiogenic outcome (24), we focused on the effects of dexamethasone pretreatment (general anti-inflammatory), gadolinium chloride treatment (macrophage inactivator) and studied Rag-1^-/- mice (T/B lymphocyte deficient). We measured inflammatory cells in bronchoalveolar lavage fluid and lung homogenate MIP-2 and Il-6 protein levels, within 24 hrs after LPAL and systemic blood flow to the lung 14 days after LPAL with labeled microspheres as a measure of angiogenesis. Blood flow to the left lung was significantly reduced after dexamethasone treatment compared to untreated control LPAL mice (66% decrease; p<0.05) and significantly increased in T/B lymphocyte deficient mice (88% increase; p<0.05). Adoptive transfer of splenocytes (T/B lymphocytes) significantly reversed the degree of angiogenesis observed in the Rag-1^-/- mice back to the level of control LPAL. Average number of lavaged macrophages for each group significantly correlated with average blood flow in the study groups (r²=0.9181; p=0.01 different from zero). Despite differences in angiogenesis, left lung homogenate MIP-2 and IL-6 did not differ among study groups. We conclude that inflammatory cells modulate the degree of angiogenesis in this lung model where lymphocytes appear to limit the degree of neovascularization, whereas monocytes /macrophages likely promote angiogenesis.