The thermal stability of detergent-solubilized reaction centers (RC) and light-harvesting B800-850 complex from Rhodobacter sphaeroides was studied by the temperature-scanning (T-scan) method in the absorbance mode and circular dichroism (CD), and by DSC. The denaturation temperatures of RC solubilized with n-octyl beta-D-glucoside (OG) and lauryldimethylamine N-oxide (LDAO) obtained by the T-scan method did not depend on wavelengths or the methods of measurement. The denaturation temperature T-d of B800-850 complex was higher than that of RC in all measurements. The values of T-d measured at various wavelengths for RC in OG was about 10 K higher than those in LDAO. The value of T-d of B800-850 complex in OG obtained by T-scan CD at 290 nm was about 7 K higher than that in LDAO. Compared with LDAO, OG has a stabilizing effect on both RC and B800-850 complex against heat denaturation.