Recently a 50 kilodalton FKBP protein (Smp50) fromthe trematode Schistosoma mansoni was produced in bacteria and shown to have biological activity. We present here in this paper a detailed investigation of the secondary structure of this protein fromCircular Dichroism(CD) and Fourier Transform Infra-red (FTIR) spectroscopic techniques. We investigated the effect of temperature, pH and salt and solvent compositions on the secondary structure of Smp50. At room temperature and in a phosphate buffer (pH 7.1) Smp50 has 26%ïÂ¡-helix, 42%ïÂ¢-structure and 31%random coil structure and at 0ïÂ°C, the amount of ïÂ¡-helix increases to 32% with a 36% ïÂ¢-structure and a 33% random coil. When the pH is lowered to 4.0 with an acetate buffer, the ïÂ¡-helix decreases to 29%. Our results indicate that the protein is not destroyed at high temperatures, retaining as much as 20 % ïÂ¡-helix even at 80ïÂ°C. From an analysis of the FTIR spectrum, Smp50 has 28%ïÂ¡-helix, 42%ïÂ¢-structure and a 30%randomcoil structure, which is in excellent agreement with the CD results. Our results indicate that the protein has an highly extended ïÂ¢-structure in solution and gives a high degree of stability to the protein based on our temperature and pH variation studies.