Peak expiratory flow rate (PEFR) was measured using the Wright's peak flow meter in 263 school boys and 275 school girls living in Lagos, Nigeria. Their ages ranged from 6.0 years to 19.0 years (mean 11.9 +/- 3.8 yrs. for boys and 11.8 +/- 3.9 yrs. for girls). Mean PEFR was 359.2 +/- 102.0 L/min (range 160.0-610.0 L/min) in boys and 327.7 +/- 81.3 L/min (range 160.0-500.0 L/min) in girls. Apart from ages 17, 18 and 19, peak expiratory flow rates were similar in both boys and girls. In both sexes, PEFR correlated positively and significantly with age, height, weight and body surface area. Also in both sexes and in all age groups studied, PEFR was significantly higher than predicted values obtained from previous Nigerian and caucasian prediction equations. When compared with values obtained from a second caucasian prediction equation, observed values were significantly higher in the 6-10 years and 16-19 years age groups in boys and 11-15 years and 16-19 years age groups in girls. New prediction equations for calculating PEFR in Nigerian boys and girls are presented. Observed PEFR may be due to enhanced stature in Nigerian children resulting from improved environment and genetic factors.