The photoacoustic (PA) technique has been employed to a number of new biomedical applications based of highly sensitive detection of laser-induced acoustic waves from individual live cells and single absorbing micro-particles or clusters of nanoparticles. These applications involve both linear and non-linear thermoacoustic phenomena initiated by focused nanosecond single laser pulse and detected with a fast PZT-ceramic acoustic transducer. Particularly, we present the following experimental results: 1) monitoring of linear and non-linear PA responses from red blood cells in suspensions in vitro ; 2) detection of PA responses from breast cancer cell targeted with gold nanoparticles; 3) PA study of linear and non-linear interaction of laser with colored polystyrene micro-particles as model single absorbers; 4) monitoring of PA responses from moving absorbers in flow in vitro (PA flow cytometry in vitro ); 5) recording of PA responses from blood flow in vivo on rat mesentery as animal model (PA flow cytometery in vivo ); and 6) monitoring of sedimentation kinetics of particles and cells. The obtained results demonstrate the high sensitivity, low background, simple detection principle, easy data acquisition, and straightforward interpretation of the PA data.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.