Drug delivery into thrombus may be achieved using the pressure transients associated with the formation and collapse of laser-induced vapor bubbles. To evaluate this delivery technique, the effects of target material, laser energy, absorption coefficient, fiber size, repetition rate, and number of pulses on the spatial distribution of delivered drug were measured. A microsecond flash-lamp pumped dye laser delivered 30-100 mJ pulses through optical fibers with diameters of 300-1000 μm. Vapor bubbles were either created on porcine thrombus in a field of 1 μm fluorescent microspheres or 1-5 mm above clear gelatin targets in a field of mineral oil containing a hydrophobic dye (D&C Red #17). The interaction of the vapor bubbles with oil and gelatin was captured using microsecond flash photography. We found that multiple pulses at lower energies reached the same depths as fewer pulses at higher energies. The greatest penetration (1-2 mm) was achieved when the gelatin or thrombus cracked or broke. The penetration was less than 500 μm when the gelatin surface remained macroscopically undamaged. Microsphere penetration into thrombus was a few hundred microns deeper than the control samples.