The usefulness of Ca alginates as matrix material for controlled release formulations was investigated with the herbicides monolinuron (1), desmetryn (2), chloridazon (3), atrazine (4), MCPB (5), simazine (6) and chloroxuron (7) as active ingredients. Release rates of these substances were measured from hydrated and dried gel beads. The results obtained indicate that release from both gel types corresponds to the water solubilities of the active ingredients. Sufficient retardation of herbicide release up to several months could be attained with the hydrated and dried Ca alginate formulations of 6 and 7 (water solubilities 5 and 3.7 ppm, respectively) and the dried formulations of 4 and 5 (water solubilities 70 and 44 ppm, respectively).