Cultures of human leukemic undifferentiated cells (named FLG29. 1) and saphenous vein internal wall were studied by IR microscopy and ATR techniques, respectively. The effect of cell differentiation into osteoclastic characteristics induced by TPA enzyme was tested. Two different pools of differentiated and undifferentiated cells, carefully washed with saline, were centrifuged on BaF2 discs, dried in a vacuum chamber and measured by an IR-PLAN' microscope. Five cell filled fields and one empty field were selected by visual inspection for sample and reference IR measurements respectively. The effect of freezing on the endothelial venous wall was tested using 5 independent segments cut longitudinally into two parts, one of which was stored for 2 hours in liquid nitrogen. The fresh and defrosted samples were gently dried by gauze imbibition and flattened on the free surface of a ZnSe crystal, for ATR measurements. In both cases JR spectra were taken at 4 cm' resolution in the range 4OOO--7OO cm' and were analyzed by measuring the peak frequency and the area beneath 14 absorbing bands. Peak frequency shifts were tested by analysis of variance. Band areas were compared by analysis of covariance, with reference to amide II band. Results. In the FLG cells spectra, statistically significant frequency shifts were found in the regions of CH3 and esthenc CO stretching (p <0.001) and in the areas of the bands peaked at 2926, 2860, 1740, 1 186 and 1087 cm' (at least p <0.02). In venous wall spectra no significant (p <0.2) effects due to freezing were revealed.