Eleven field experiments, six on Upland (Gossypium hirsutum L.) and five on Pima (G. barbadense L.) cotton, were conducted from 1988 through 1990 in Arizona to evaluate the response to several treatment regimes of Mepiquat Chloride (PIX(TM)). Each experiment had 7 treatments arranged in a Randomized Complete Block Design in the field with a minimum of three replications. The 1988 and 1989 studies utilized low rate multiple applications of 1/8 pint PIX/acre to 1 pint PIX/acre early in the first fruiting cycle before peak bloom. In an effort to define plant conditions prior to and after PIX applications, plant measurements were taken on approximately 14 day intervals for the following parameters: plant height, mainstem node number, flower numbers per 25 feet of row, number of nodes above the top white bloom, percent canopy closure, plant mapping and heat units accumulated after planting (HUAP). Findings from these studies identified the ability of PIX to reduce plant height, about 13% compared to control plants, when application rate was 1/2 pint PIX/acre or greater. It was also found that plant height reduction was short term, lasting about two to four weeks after PIX applications. Based on the 1988 and 1989 studies, the 1990 treatment strategy was revised to increase the rate of applications and to extend the applications period beyond peak bloom to prolong the short term effects of PIX. The 1990 results indicated that this change in strategy for PIX multiple applications has merit. The three years of multiple application experiments show that more positive results are seen in association with higher application rates combined with an extended period of application dates. Results also support the basis of initiating PIX applications in response to measurable plant parameters which are indicative of vegetative growth tendencies, rather than pursuing a pre-determined PIX treatment program irrespective of actual crop conditions. Inadvertent applications of PIX, which may not be warranted in relation to crop development, can potentially result in yield losses due to a limitation in structural growth and fruiting site development. Easily obtainable plant measurements such as plant height (inches): mainstem node ratios and percent fruit retention from plant mapping data (first two positions per fruiting branch), represent two crop parameters being used in the development of guidelines and recommendations associated with PIX applications on cotton in Arizona. These research projects have been and will continue to be oriented towards guideline developments in relation to the three fundamental questions associated with PIX use on cotton: 1) when should PIX be applied? 2) what application strategy should be used? (multiple or single)? and 3) what rates should be used? Some progress in this area has been realized but further research and evaluation is still in order for Arizona cotton production conditions.