By using a flow microcalorimeter system, enthalpies Delta H-0 of binding or complex formation were determined in aqueous solutions for the following systems; self-association of a-chymotrypsin, bindings of 2-pyrrolidone and poly (N-vinyl-2-pyrrolidone) with hydrocarbon cosolutes, and complex formations in cyclodextrin-guest molecular systems. The other thermodynamic parameters, Delta G(0) and Delta S-0, were evaluated by the theoretical relations. A critical comparison of these parameters with the reported ones based on equilibrium methods were given. Significant dissimilarities were shown between two. It was assumed that these calorimetric determined parameters are much inclined to reflecting solution and binding states in aqueous solution.