The aim of the present study was to describe the long-term sequential changes of the acute phase proteins and of commonly used so-called nutritional markers in patients with community-acquired pneumonia (CAP), and to calculate the normalization rate of serum C-reactive protein (CRP), defined as the time for a 50% decrease, during the initial treatment of these patients. The long-term sequential changes of inflammatory and nutritional markers in patients with CAP have not been previously well-documented. However, in the diagnostic work-up of patients with suspected infectious diseases CRP levels are often used nowadays. Serum albumin, transthyretin (prealbumin), and transferrin together with serum iron, have often been used as "nutritional markers" in patients. We therefore studied the long-term changes of these parameters in patients with CAP, as these markers also are influenced by inflammatory reactions, in pneumonia for example. All the patients within the age range 50-85 years, with the exception of immunocompromised patients, who were admitted with CAP to the Department of Infectious Diseases at Danderyd Hospital during a 12-month period (January 1992-January 1993), were reviewed for inclusion in a prospective study of the long-term sequential changes of inflammatory and nutritional markers in CAP patients. A total of 97 patients (50 men) with a mean age of 69.6 years were included in the study. Blood samples were drawn on admission, during the hospitalization period, and at the follow-up visits. Serum CRP, alpha 1-antitrypsin, haptoglobin and orosomucoid (alpha 1-acid glycoprotein) were used as acute phase proteins. However, albumin, transthyretin, and transferrin together with serum iron and percentage transferrin saturation were also included. Of all the parameters studied, CRP showed the greatest variation, already having the highest values at admission. CRP also showed, together with iron, the earliest response to recovery in the patients. The median time for a 50% decrease of CRP was 3.3 days for the patients (n = 73) with more than two CRP values measured during the first nine days. Transthyretin responded faster to patient recovery than did albumin. CRP showed the greatest amplitude of changes and together with iron and percentage saturation of transferrin it also showed the earliest response to recovery in patients with CAP. This indicates that CRP is the best of the parameters studied for use in diagnostic work-up and in follow up.