Rhodococcus equi is a well-established pathogen in foal pneumonia and is increasingly recognized as a pathogen in immunocompromised humans. We have isolated a Gram-positive coccobacillus from 8 blood samples and lung tissues of a renal transplant patient. Colony morphology, growth in Lowenstein-Jensen medium, 21 biochemical reactions, the characteristic morphological cycle (coccus-rod-coccus) and the CAMP test established the R. equi diagnosis. Histological studies of 2 lung biopsy specimens revealed numerous microabscesses with aggregates of polymorphonuclear leukocytes surrounded by abundant foamy macrophages. Our isolates proved to be sensitive to majority of antibacterial drugs. The appropriate therapy (amoxicillin-clavulanate) proved to be effective, however six months later a relapse was observed. Data show that in spite of its rare occurrence, R. equi infection represents a diagnostic and therapeutic challenge. The taxonomical, epidemiological, clinico-pathological, diagnostic and therapeutic data of R. equi are discussed.