(1) As previously shown, stereospecific binding of opiates to membrane bound receptors is inhibited by treatment with small amounts of phospholipase A2 from Vipera russelli. This effect is quantified and compared with the enzymes from the venoms of Naja Naja siamensis, Apis Mellifica and from porcine pancreas. All enzymes are equally effective. The inhibition is due to partial phospholipid hydrolysis leading to inactivation of membrane-bound receptor. (2) Bee venom phospholipase A2 together with the synergistically acting peptide, melittin, causes receptor solubilization up to 80% of preformed receptor-ligand complex can be solubilized in this manner. (3) Lysophosphatidylcholine, a product of phospholipid hydrolysis, solubilizes performed receptor-ligand complex to a similar extent. Several other detergents were tested for their ability to solubilize receptor-ligand complex. Digitonin appears to be most effective in solubilizing such a complex.