It has frequently been assumed that hydrophobic surfaces serve as initiation points for in vivo bubble formation; yet, no studies have demonstrated that this relationship actually exists. In the present investigation, the concept of spontancous bubble formation at smooth hydrophobic surfaces has been examined. Smooth polystyrene and silica beads, each with either hydrophilic or hydrophobic surfaces, were examined for their ability to generate bubbles in distilled water at gas supersaturations ranging from 5 to (125 \mathrm{~atm} \mathrm{~N}{2}) at room temperature (\left(24-27^{\circ} \mathrm{C}\right)). Few bubbles occurred in suspensions exposed to gas supersaturations in the range from 5 to (50 \mathrm{~atm} \mathrm{~N}{2}). Even at higher gas supersaturations, which approached the spontancous nucleation threshold of bulk water, relatively few bubbles were formed in these suspensions. Clearly, these surfaces did not induce gas bubble formation, even at high gas supersaturations. This suggests that the cohesive forces between the water and hydrophobic particles were not weakened to the point of rupture, so that these interfaces did not provide bubble nucleation sites. This investigation demonstrated that smooth surfaces, whether hydrophilic or hydrophobic in nature, do not facilitate in vitro gas bubble formation by dissolved gas in water. (1993 Academic Press. Inc.