We report an experimental study on transient membrane permeabilization of single living bovine aortic endothelial cells (BAEC) by tightly focused femtosecond near-infrared laser pulses. The membrane permeabilization of the BAEC cells was studied as a function of the incident laser intensity. The rate of dye uptake by the cells was analyzed using time-lapse imaging. We found that membrane permeabilization occurs for laser intensities higher than 4.0 x 10(12) W/cm(2). For laser intensity above 3.3 x 10(13) W/cm(2) the cell disintegrates. Within these two limits the rate of dye uptake increases logarithmically with increasing laser intensity. This functional dependence is explained by considering the Gaussian intensity distribution across the laser focal spot. Cell membrane permeabilization is explained by the creation of a plasma within the laser focal spot. The physical understanding of the relationship between dye uptake, pore characteristics, and laser intensity allows control of the concentrations of molecules delivered into cells through the control of pore characteristics.