In this work we use infrared spectroscopy to investigate solubility properties of a bioactive substance in supercritical CO2 (scCO(2)). By using acetaminophen as a model compound, we show that the method can provide high sensitivity that makes it possible to study solubility at small concentrations, up to 10(6) mol.L-1. This method also allows one to investigate the kinetics of the dissolution process in supercritical solvent. Our measurements at two different points of the (p,T) plane ((40 MPa, 373 K) and (40 MPa, 473 K)) have shown significant difference in the kinetic mechanisms of acetaminophen dissolution at these two states: at higher temperature the dissolution process in scCO(22)has two steps: (i) fast step when the acetaminophen concentration in scCO(2) quickly reaches (70 to 80) % of the saturation level and (ii) a subsequent slow step where the acetaminophen concentration slowly increases up to the saturation level. However, at lower temperature, the dissolution process has only one, slow step.