Ten subjects from the Forsyth County, North Carolina, and Washington County, Maryland, field centers in the Atherosclerosis Risk in Communities Study had two fat tolerance tests within a 10-day period from September 1988 to February 1989 to determine the reproducibility of markers for postprandial lipemia. No significant differences between visits were found in fasting mean plasma lipids, lipoproteins, and apolipoproteins. Postprandial triglycerides and retinyl palmitate were measured at 3.5 and 9.0 hours after the test meal in whole plasma. There were no significant differences in the mean levels of these analytes between visits. The correlation of triglycerides between repeat visits at 9.0 hours (r = 0.87) was stronger than in fasting samples (r = 0.67) or at 3.5 hours (r = 0.69). The mean plasma retinyl palmitate level at 3.5 hours was 15% higher than at the 9.0-hour level. The correlation of repeat measures of retinyl palmitate at 9.0 hours (r = 0.94) was much stronger than at 3.5 hours (r = 0.79). In conclusion, estimates of reliability in postprandial measurements of 9.0-hour triglycerides and retinyl palmitate levels were as strong as fasting lipid measurements of total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol, and high density lipoprotein cholesterol, and both postprandial triglyceride measurements exceeded that of fasting triglyceride (r = 0.67).