Time-resolved in vivo measurements have been performed to determine the optical properties of the female breast. The optical parameters at 800 nm are of special interest for medical diagnosis since this wavelength is close to the isosbestic point of oxy- and deoxyhemoglobin. The measurements have been performed with a Ti:sapphire laser using a synchroscan-streak camera. The diffusion model has been used to calculate the absorption coefficient (mu) A and the reduced scattering coefficient (mu) 's equals (mu) s (1 - g). Measurements at different positions on the mamma showed systematic changes of the time-resolved signals which can be explained by the composition of this heterogenous tissue. A good agreement between the measurements on the right and left mamma has been found. Additionally, time- resolved experiments on breast tissue in vitro at 532 nm, 800 nm, and 1064 nm have been performed to study the optical properties at these wavelengths.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.