Dietetic, hematologic and biochemical data were used to asses the iron status of a group of 64 adolescents (37 males and 27 females), aged 15 to 18 (mean age 15.94 +/- 0.76 years), who study in a High School in the comunidad Autónoma de Madrid. All were asked to keep a dietary record during 5 days, one of which had to be a sunday. Iron intake was estimated using the Food Composition Tables of the Instituto de Nutrición (1990). The hematologic survey determined hemoglobin hematocrit mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), serum iron and serum ferritin. These data were correlated with the scores obtained in the attention and school capability test (AT), that gave information about the verbal (V), reasoning (R) and calculus (C) capabilities. There is a positive correlation between MCV (r = 0.2705), MCH (r = 0.3370) ferritin (r = 0.3383) and attention. MCV (r = 0.2995), MCH (r = 0.3998), MCHC (r = 0.3134) and ferritin (r = 0.3970) were also correlated with the speed capability shown on the attention test and the hemoglobin level was correlated with the calculus capability (r = 0.2905). The students who obtained higher scores in the school capability test had also better blood parameter values. This was statistically significant for serum ferritin in males students and for hemoglobin and MCHC in female students. 19.6% of the adolescents had ferritin levels lower than 12 ng/ml. Their intelligence test scores were lower to those who had serum ferritin > or = 12 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)