Sera and questionnaire data from a population-based random sample of healthy adults was used to evaluate factors influencing neopterin and beta 2-microglobulin (beta 2m) values. Both neopterin and beta 2m levels increased with age and were higher among white than blacks (mean values for whites and blacks: neopterin, 5.06 vs 4.49 nmol/L; beta 2m, 1.36 vs 1.28 mg/L). Gender differences were noted for beta 2m but not neopterin values (beta 2m males vs females: 1.37 vs 1.29 mg/L). Neopterin values were lower among current smokers than among nonsmokers (4.32 vs 5.16 nmol/L) and were higher among users of antihistamines (5.46 among users vs 4.65 nmol/L among nonusers). Neopterin and beta 2m were correlated in this healthy adult population (adjusted r = 0.53, P = 0.001), yet no other interrelationships with numerous biologic markers except between beta 2m and serum-soluble interleukin-2 receptor levels (adjusted r = .41, P = 0.05) were observed. These findings provide important baseline information to consider before planning or evaluating studies utilizing neopterin or beta 2m levels
