Correlations between semiquantitative amounts of Pneumocystis carinii (PC), the degree of inflammation, and the severity of pneumonia were analyzed in 58 patients with PC pneumonia (PCP). Material from both transbronchial biopsies (TBBs; n = 39) and bronchoalveolar lavage fluid (BALF; n = 57) was examined. In the TBB the amount of PC correlated strongly with overall inflammation in the interstitium (Kendall correlation coefficient [Kcc] = 0.59; p < 0.0001), type 2 pneumocyte proliferation, and edema formation. The amount of PC in the TBB also correlated with interstitial accumulation of neutrophils (Kcc = 0.54; p = 0.0001), lymphocytes, and macrophages. In BALF the amount of PC correlated with edema formation and type 2 pneumocyte proliferation in the TBB but not with the percentage of neutrophils, lymphocytes, or macrophages in BALF. The amount of PC in the BALF and the percentage of neutrophils in the BALF correlated significantly with Po2 and the serum lactate dehydrogenase (LDH) level. Neither short-term nor long-term survival was affected by the amount of PC, inflammatory markers in the TBB, inflammatory cells in BALF, Po2, or the serum LDH levels. In conclusion, the amount of PC is associated with the extent of the acute inflammatory reaction in the lung in PCP associated with human immunodeficiency virus (HIV).