Scanning electron micrographs that depict the surface and internal structure of several starch-encapsulated granular formulations of EPTC (S-ethyl dipropylthiocarbamate) and butylate (S-ethyl diisobutylthiocarbamate) relate well with herbicidal release rates previously reported. Fast-release formulations appear to have a porous surface with little distinctive internal structure. Diffusion would be expected to be more rapid as fewer diffusion barriers are present. Slow-release formulations have a smooth, hard surface with irregular surface pores and a honeycombed internal structure. The slower release characteristics are associated with stronger oxidants used for crosslinking xanthate in the entrapment of herbicides. The scanning electron microscope would be an excellent quality control technique in the preparation of starch-encapsulated herbicides.