Sixteen Acala seed stocks were planted in eight different experiments over a three year period. Nine of these represent succeeding commercial releases dating back to 1939. The remaining entries were forerunners of these cottons though most were never planted commercially in California. In the 40 year period from 1939 to 1979 genetic advances resulted in a yield gain of one third, or an average of eight pounds of lint/acre per year. Failure to translate genetic gains made since 1960 into commercial production suggests increased environmental constraints coming into play. Of the fiber characteristic measured, length has increased significantly since the late fifties, strength has steadily increased throughout the period and micronaire has remained in a relatively narrow but desirable range since the release of Acala 4-42 in 1949.