AbstractBackground and ObjectivesThermal effects of laser radiation at cell level play very important role in cell functioning and in many laser applications. The aim of this study was to evaluate a new method of photothermal imaging (PTI) for monitoring short‐time nano‐scale thermal effects in individual living cells.Study Design/Materials and MethodsPTI is based on the irradiation of a cell with a short laser pump pulse (8 nanoseconds, 532 nm) and on registration of the laser‐induced local thermal effects using time‐resolved phase‐contrast imaging with a pulsed probe laser.ResultsPT images of lymphocytes, lympholeukemia cells in vitro were obtained at different laser energies. PTI in time‐resolved mode allowed visualizing the structures with size less than diffraction limit (90‐nm liposomes). The photodamage process was visualized for a single human leukocyte in suspension.ConclusionsPTI in non‐invasive mode offered better contrast of living cell image than conventional optical phase‐contrast microscopy. The data obtained showed that PTI is in perspective for studies of live non‐fluorescent cells. Lasers Surg. Med. 31:53–63, 2002. © 2002 Wiley‐Liss, Inc.