The influence of operating parameters and fluid characteristics on the steady-state flux during cross-flow microfiltration was studied. An equation to predict flux, which related the influence of various factors on flux, was determined by studying latex. An exponential relationship between the steady-state flux, Jss, and the factors was found and expressed as follows : J(SS)=V-L=K.u(1.0).C-p(-0.5).d(p)(-0.67).eta(-1.0), where V-L, u, C-p, d(p) and eta are the lift velocity, feed velocity, particle concentration, particle size and viscosity, respectively; This equation was found to be applicable to the filtration of baker’s yeast, Bacillus caldolyticus M1, and methanogenic waste. The filtration constant K, as defined by the equation, was the same (3x10(-4) kg(0.5).m(-2.17).Pa.s) for the filtration in each case, while it was different for latex. This difference can be explained by estimation of the water content of the particles, which allows a correction to be made in particle concentration (C,).