The aim of this study was to evaluate whether the amount of Pneumocystis carinii organisms found at fiberoptic bronchoscopy (FB) performed on HIV-positive patients correlated to the character of the P. carinii pneumonia (PCP). A consecutive series of 105 patients presented with 131 episodes of pulmonary symptoms requiring FB, and in 75 of these episodes a diagnosis of PCP was made. Specimens were stained with Giemsa and methenamine silver nitrate and the number of parasites found was given as: numerous, many, few or none. The following signs and symptoms were registered: cough, dyspnoea, fever, loss of weight, chest radiograph, haemoglobin, WBC, CD4 cell count, PO2 and HIV p24 antigen. The PCP was characterized by the clinical course: mild, moderate, severe, and by the outcome: pulmonary healthy, pulmonary insufficiency and death. No correlations between the number of P. carinii organisms and the clinical course or outcome of the PCP, the symptoms before the FB or the paraclinical examinations were found. In conclusion, the routinely obtained quantitative results of the microbiological examinations of material from the lungs were not correlated to the severity of the PCP.