Diabetes mellitus is characterized by hyperglycemia, a relative lack of insulin. The metabolic disturbances in diabetic patients are often associated with cardiac and liver dysfunctions. Generally, experimental diabetic models in animals have been used to study diabetes-related changes in organ function, but the complexity of intact tissues can cause contradictory results. For this reason, different techniques have been used to understand the mechanisms of these dysfunctions in diabetic organs. The purpose of the present study is to investigate the effects of streptozotocin (STZ)-induced diabetes on rat liver and heart tissues at the molecular level by Fourier Transform Infrared (FTIR) spectroscopy. Wistar rats of both sexes, weighing 200-250 g, were made diabetic by a single injection of 50 mg kg(-1) intraperitoneal (i.p.) streptozotocin dissolved in 0.05 M citrate buffer (pH 4.5) and they were kept for 4-5 weeks. The diabetes status was checked by measuring the blood glucose level. In the complex FTIR spectra, the bands in the C-H region for example the CH2 antisymmetric and symmetric stretching, the CH3 symmetric and asymmetric stretching vibrations due to lipids and proteins in the 3000-2800 cm(-1) region and CH2 scissoring around 1464 cm(-1) and the CH3 scissoring at 1454 cm(-1) were analyzed. Characteristic spectral bands of these diabetic samples were compared with those of control group to confirm the effect of diabetes on liver and heart tissues. The FTIR spectra revealed dramatic differences in the band positions and bandwidths, signal intensity values and signal intensity ratios between diabetic and control tissues. Similar differences were observed for diabetic liver and heart tissues. A significant increase in the bandwidth of the CH2 symmetric and antisymmetric stretching and the CH3 symmetric and asymmetric stretching bands has been observed for both tissue types. The wavenumber of the CH3 asymmetric stretching band shifts to lower values, indicating an increase in the order in the deep interior part of the lipid chains. The ratio of the CH2 symmetric to CH3 symmetric stretching band (lipid/protein ratio) decreases by 13% for diabetic heart and river tissues. A decrease is also detected in the ratio of the CH2 scissoring to the CH3 scissoring mode. The overall intensity of these bands is seen to increase for diabetic tissues. (C) 2000 Elsevier Science B.V. All rights reserved.