The application relates to means for diagnosing, predicting or monitoring Pneumocystis pneumonia (PCP). The means of the application are also suitable for determining or predicting the efficacy of a drug or treatment against PCP in a human patient. The means of involve the detection and/or quantification, more particularly the quantification, of the RNA transcripts of two different P. jirovecii mitochondrial genes. The first of said two P. jirovecii mitochondrial genes is the P. jirovecii gene, the sequence of which codes for the Cytb protein or the P. jirovecii mitochondrial Small Sub-Unit (mtSSU) gene. The second of said two P. jirovecii mitochondrial genes is a P. jirovecii gene, the sequence of which transcribes into a P. jirovecii ribosomal RNA, e.g., be the mitochondrial P. jirovecii Large Sub-Unit (mtLSU) gene.