The objective of this study was to evaluate the sensitivity of C-reactive protein (CRP) elevation compared to erythrocyte sedimentation rate (ESR), leucocyte count and thrombocyte count in the diagnosis of infective endocarditis (IE). It was designed as a prospective study of suspected episodes of IE in adults in tertiary care at a university-affiliated department of infectious diseases. In 89 episodes of IE, CRP was available from the start of treatment. Median age was 66 years, 45 were men and 44 women. Median CRP concentration was found to be 90 (range 0-357) mg/l with only 4% normal values. Episodes involving native valves had higher CRP than episodes occurring with prosthetic valves. Staphylococcal origin, short duration of symptoms, short duration of fever and highest recorded temperature all correlated to higher CRP levels. The CRP response was also prominent among patients > 70 years old. Among non-responders, a few cases with simultaneous cirrhosis were noted. ESR was less sensitive than CRP, with a normal level in 28% of the episodes. It was concluded that CRP determination is superior to erythrocyte sedimentation rate, leucocyte count and thrombocyte count in the diagnosis of infective endocarditis.