Rice cells derived from PI 353705 (similar to Assam 5) were isolated from anthers cultured on Blaydes medium containing IAA, 2,4-D, kinetin, yeast extract, and coconut milk. Isolated aggregates of cells were plated on a modified Blaydes medium containing 10−3 M S-aminoethyl-l-cysteine (S-AEC). This level ofS-AEC inhibits nonselected wild type cells. Cells or aggregates of cells resistant to this analog of lysine were subcultured three times in the presence of 2×10−3 M S-AEC. The selected cells were then placed on a Murashige-Skoog (MS) regenerating medium containing 1 mg/l each of IAA and kinetin. Ten plants were recovered from 34 selected cell lines, three plants grew to maturity, and two produced seeds. Seeds from plants regenerated from cells in culture had higher lysine than the original field controls and had increased levels of free alanine, arginine, and asparagine. The in vitro selection produced plants with higher protein than the field controls. Plant breeders have begun to evaluate the genotype recovered from in vitro selection.