The temperature induced effects of fish oil on dipalmitoyl phosphatidylcholine (DPPC) model membranes (fish oil/lipid ratio: 2% w/w) were investigated by Fourier transform infrared (FTIR) smd UV/Visible spectroscopic techniques. In FTIR study the C-H and C=O stretching modes were investigated. The results of the FTIR study reveals that fish oil changes the physical properties of the DPPC multilamellar liposomes by broadening the phase transition profile and increasing the bandwidth of the CH2 stretching bands. Those results imply respectively that fish oil interacts with the cooperativity region (C2-C8) of the fatty acyl chain and increases the dynamics of the acyl chains. At this fish oil/lipid ratio, fish oil decreases the main phase transition temperature to lower degrees. No significant change in the frequency of the CH2 stretching bands is observed implying that fish oil does not change the number of gauche conformers, i.e., does not make any significant effect on the order of the membrane. Investigation of the C=O band reveals that fish oil does not make hydrogen bonding with the C=O group of phospholipid. Turbidity studies were performed at 550 nm. With the addition of fish oil, main phase transition temperature shifts to lower degrees and a dramatic decrease in absorbance values were observed indicating that fish oil increases the fluidity of the membrane. The results of turbidity studies are consistent with the FTIR study. (C) 1999 Elsevier Science B.V. All rights reserved.