This study investigated the levels of C-reactive protein (CRP) and prealbumin in 87 infants suspected of dying from sudden infant death syndrome (SIDS). These proteins change rapidly, within 24 hr, in patients who have an acute phase response, especially a response resulting from bacterial infection. In addition, prealbumin is sensitive to a recent reduction of protein or calorie intake. Eighty patients were determined to have typical SIDS. Only four of these had a minimal increase in CRP (0.8-2 mg/dl), and in none could an explanation be found. Seven patients were uncovered who had a significant infection, four of whom had prominent CRP elevations. Prealbumin was not decreased in the SIDS population. We conclude that there is no evidence that the acute inflammatory response is activated in infants dying of SIDS. An elevation of CRP above 2 mg/dl should prompt additional studies to find the cause. There is also no evidence of a recent, significant decrease in nutrition in these patients.