 a review of the literature indicated an association among high nitrate ingestion , methemoglobinemia , and pathologic changes in bronchi and lung parenchyma . 
 the present study examined a possible correlation among drinking water nitrate concentration , methemoglobin levels , cytochrome b(5 ) reductase activity , and acute respiratory tract infection with a history of recurrence ( rrti ) . 
 our study was conducted in five village units in the state of rajasthan , india , with nitrate concentrations of 26 , 45 , 95 , 222 , and 459 mg no(3 ) ion / l . 
 we randomly selected 88 children . 
 the children were up to 8 years of age , age matched , and represented 10% of the total population of these areas . 
 we obtained detailed rrti histories and conducted medical examinations . 
 methemoglobin levels and cytochrome b(5 ) reductase activity were estimated biochemically . 
 the data collected were statistically analyzed using spreadsheet software on a personal computer . 
 we observed strong interdependence between methemoglobin levels and rrti in children up to 8 years of age . 
 methemoglobin levels alone explained 80% of the variation in the rrti cases . 
 this study indicates that methemoglobinemia , secondary to high nitrate ingestion in drinking water , causes rrti . 
 increased production of methemoglobin and free radicals of nitric oxide and oxygen due to nitrate metabolism in the body lead to alveolar damage and mismatching of ventilation and perfusion , which may be the reason for high mortality in children due to rrti.imagesfigure 1 
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