Equilibrium dialysis experiments done at 37°C showed that equilibrium of delta-9-THC is attained at 60 hr using optimum concentrations of delta-9-THC (≤ 1 x 10-5 M) and bovine serum albumin (BSA, 1 x 10-6 M) in Na-phosphate buffer of varying concentrations and pH. At higher concentrations (> 1 x 10-5 M), delta-9-THC did not attain equilibrium even after 70 hr of dialysis at 37°C. The maximum binding of delta-9-THC to BSA takes place in 1 x 10-2 M Na-phosphate buffer, pH 6.5. At buffer (pH 6.5) concentrations above and below 1 x 10-2 M and also with the variation of buffer pH (irrespective of the concentration), the binding of delta-9-THC to BSA is significantly decreased. The isotherm for the binding of delta-9-THC (≤ 1 x 10-5 M) to BSA (1 x 10-6 M) in 1 x 10-2 M Na-phosphate buffer, pH 6.5 at 37°C is double sigmoid in nature. Scatchard plot shows that the total number of available binding sites per molecule of BSA(n) at lower concentrations of delta-9-THC (≤ 6 x 10-6 M) is five, and the binding constant (K) is 2.28 x 106 M-1. At relatively higher concentrations of delta-9-THC (> 6 x 10-6 M) an absurd negative value of K is obtained. These results suggest that there are at least two types of delta-9-THC binding to BSA molecule.