Two new optical methods for measuring size and velocity of quasi-spherical biological particles are proposed. One is an optical correlation method, based on the transformation of the transverse coherence function of the scattered field which forms the scattering particle images. A device for measuring the scattering particles size distribution function is proposed which has a response time of about 10 seconds, and can be applied to measure particles having sizes in the range of 3 to 500 micrometers to within 10%. The other is a holographic continuous exposure method for studying the dynamical and structure characteristics of the Brownian motion of unicellular algae. The measured algae velocity and size distribution functions are reported.