Estudos sôbre a conservação de sementes: I. - Respiração de sementes de algodão em diversas umidades relativasCotton seeds subjected to relative humidities varying from 10 to 100% were studied regarding their intensity of respiration. Pettenkoffer tubes were employed, so that one could works simultaneously with 6 of them. H2SO4 solutions controlled the relative humidities. Respiration was found to be noticeable obove 80% relative humidity. Cotton seeds kept under relative humidities varying from O up to 90%, exibit seed-humidities which varied from 1,10 to 20,97%.