Calcium alginate gel beads containing insect repellent N,N-diethyl-3-methylbenzamide (CAGBDs) were modified via grafting copolymerization with a vinyl monomer. CAGBDs (5 g) were initiated with 8.5 x 10(-2) mol/L potassium persulfate and 7.0 x 10(-2) mol/L sodium bisulfite at the ambient temperature for 10 min, and then 6.22 mol/L acrylonitrile was added in droplets; the mixture was allowed to react at the same temperature for another 30 min. The effects of reaction conditions such as the stirring speed and monomer concentration on the modification of CAGBDs were investigated. Scanning electron microscopy analysis showed that the surface of modified CAGBDs was compact enough to keep N,N-diethyl-3-methylbenzamide from touching. The release rate of N,N-diethyl-3-methylbenzamide from modified CAGBDs was slower than that from unmodified CAGBDs. (c) 2006 Wiley Periodicals, Inc.