Electrophoretic patterns of hemoglobins, Root effect, Bohr effect in blood and stripped hemoglobin, Hb-O2 affinity GTP modulation of Astyanax scabripinnis (lambari), caught at three different altitudes in Ribeirão Grande, near Campos do Jordão (São Paulo), are described. All populations showed the same electrophoretic patterns: two cathodal components in starch gel. Normal Bohr effect values were found in these three populations both in blood (phi = -0,11) and stripped hemoglobin (phi = -0,12). Different blood O2 affinities collected in fish of these 3 populations were detected. GTP has a large influence on Hb-O2 binding properties in A. scabripinnis. Stripped hemoglobin shows small Root effect. The addition of triphosphated nucleotides increases this effect. GTP is more effective than ATP on enhancing Root effect. Oxygen availability in water can be the factor responsible for differences found in blood O2 affinity.