We describe the use of the optical trapping technique to the study of micron-sized particles and cell samples, from which scattering, particle size, and optical parametric data can be derived. Its application to the study of phytoplanktonic cells and other biogenic particles is also presented. In comparison to conventional flow cytometric or volume scattering measurement systems, an optical trap utilizes the radiation forces, derived from a highly focused laser beam, to confine the particle under study to an optical potential well. The optical trap, therefore, functions simultaneously as both a non-contact micromanipulator and microforce transducer. In addition, forward angle light scattering measurements can be made while the cell sample is held by the focused laser beam. Forward light scattering measurements and calculations for optically trapped spherical test particles and mammalian cells, under low power (< 10 mW), are presented for the cases when the laser beam spot size (omega) o is approximately r, (lambda) /2n < (omega) o < r, and (omega) o approximately (lambda) /2n, respectively, where r is the cell radius and n is the refractive index of the surrounding water medium. Scattering data over the range from approximately 0 degree(s) to 45 degree(s) is shown to be a sensitive function of beam radius, particle size, and relative refractive index. The optical trapping technique should prove to be a powerful tool in the study of the optical properties of marine cells and organisms, and their dependence on external optical stimuli.