Concentrations of serum folate, red cell folate and serum cobalamin were studied among 240 normal healthy Nigerian adolescents aged 12-17 years. Serum folate level was generally low with a mean of 2.8 nmol/l while red cell folate level was not low with a mean of 369 nmol/l. Mean serum cobalamin was 615 pmol/l. A negative significant correlation was observed between serum folate and red cell folate among the adolescents (r = 0.24). Another significant correlation was observed among the 14 year olds between red cell folate and serum cobalamin (r = 0.404). The folate parameters were significantly lower in the adolescents with HbAS genotype with mean serum folate of 2.2 nmol/l and red cell folate of 326 nmol/l but these differences were more marked among the girls. All the girls in the study had significantly higher serum cobalamin than the boys (p less than 0.001) but the advantage of this is not clear. These results suggest that serum cobalamin may be under some hormonal influences and the high values indicate that cobalamin may be involved in other metabolic functions from the puberty period.