The solubility of imipramine HCl in supercritical carbon dioxide has been measured experimentally by a gravimetric technique. An ISCO extraction apparatus was modified to carry out the measurements. It consists of a syringe pump, a thermostatic chamber, an equilibrium cell, a variable-flow-rate restrictor, and an ice trap. Experiments were conducted by allowing the supercritical carbon dioxide to slowly flow through the cell, where the imipramine HCl had been previously loaded. The pressure was kept constant, controlled by the pump, and so was the flow rate, controlled by the restrictor. The amount of solute collected in the trap was measured in two different ways for consistency: gravimetrically and by dissolving the solute collected in methanol and measuring the concentration spectrophotometrically. The amount of solvent was measured by the difference in volume readings in the syringe pump (calculating the density of carbon dioxide at the pump conditions); this value was also determined by measuring an average flow rate of the expanded solvent and the time of the run. A total of 52 measurements were done. Two five-point isotherms, at 40 and 50 degreesC, were obtained for pressures ranging from 30 to 50 MPa. Measured solubilities were within the range (5-10) x 10(-6) mole fraction. These are the only published data for this system.