The accumulation rate and equilibrium partitioning behavior of the pesticide atrazine between water and two solid phase microextraction (SPME) fibers, polydimethylsiloxane (PDMS) and polyacrylate (PA), are presented. The more polar PA is found to accumulate atrazine to a greater extent than does PDMS. The solid phase-water partition coefficient, Ksw, for atrazine is 210 for PA and 55 for PDMS. The accumulation rate constant increases as the rate of solution stirring is increased. This result confirms that the rate of accumulation of atrazine in both PDMS and PA is limited by diffusion in the aqueous medium. Accordingly, these solid phases are useful for studying the speciation dynamics of atrazine in aqueous media.