The usefulness of calcium alginate as a matrix material fur controlled release formulations of 1-naphthalene acetic acid as a plant growth regulator and of pentachlorophenol as a herbicide was investigated. Release rates of these active agents were measured using a UV spectrophotometer from dried gel beads. Also the use of poly(ethylene imine) (PEI) as a coating substance for the alginate beads was investigated. The results obtained from these studies indicated that release from the gel beads after coating with PEI was markedly retarded. The release rates were varied completely due to post-treatment with PEI. The release was found to be dependent on the pH of the aqueous release medium; it was slower in the acidic medium.