The hypothesis tested was that gas bodies capable of nucleating violent cavitation activity in vitro would survive the rapid disruption of Albunex microspheres by 1-MHz ultrasound. Human erythrocyte hemolysis was used as a proxy measure of cavitation. Fluid (5% human serum albumin [HSA]) with or without Albunex (ALX) was exposed or sham-exposed to 1-MHz ultrasound (P+ = 1.25 +/- 0.01 MPa, P- = 0.81 +/- 0.01 MPa; ISPTP approximately 35 W/cm2) for 60 s using 10-microseconds pulses and a duty factor of 0.5. An equal volume of whole human blood was then added to the fluid, followed by a second 60-s treatment. Insonation of cell suspensions prepared in previously sham-exposed HSA + ALX fluid produced about 4% hemolysis, a level significantly greater than in the controls. Insonation of cell suspensions prepared in previously insonated HSA + ALX fluid produced about 0.4% hemolysis; this also differed significantly from the controls. The data thus support the hypothesis.