The association equilibrium of complex formation between serum albumin (bovine, rat, rabbit, guinea pig, horse, mouse and chicken) and L-methamphetamine (MAMP) was determined by the use of ultrafiltration to examine the effect of animal species on adsorption of L-MAMP to albmin. Serum albumin L-MAMP complexes had the same Scatchard plot patterns in all species tested. The binding parameters of each association equilibrium were estimated by Rosenthal's method. One kind of binding site and non-specific binding sites were distinguished in terms of the association equilibrium between each serum albumin and L-MAMP in all species tested.