In food industry there are used substances from azoic dyes such as carmoisine and tartrazine. Therefore we decided to verify by a histological study, the effect of these two dyes, administered in drinking water in concentrations of 1, 2 and 3% for 3 weeks, on liver and kidney in guinea pigs. At the end of the experiment animals were euthanized and pieces of liver and kidneys were collected and histologically processed through inclusion in paraffin. For both liver and kidney we observed phenomena represented by stasis and oedema, congestion, hepatocyte and kidney apoptosis, with atrophy of renal corpuscles. Magnitude and severity of histopathological aspects observed were directly proportional to the concentration of the administered dyes.