Studies were conducted in California's San Joaquin Valley to evaluate the rate and timing responses of mepiquat chloride on Pima cotton. Early data collected in 1991 and 1992 suggest applications made at early bloom are not economical and occasionally result in a yield decline while later applications have tended to have more positive results. The best yield response to date has come from mid- and late-bloom sequential applications of mepiquat chloride (PIX) at a rate of 0.022 lbs ai/acre applied 10 to 14 days following first bloom and again 14 days following first application. The average rate response from this treatment exceeded 50 lbs lint/acre.