Harvest aids are important in preserving cotton quality by facilitating a timely harvest. Harvest aids enhance defoliation of plant leaves, accelerate boll opening, improve seed-cotton drying in the field and, in some cases, desiccate green plant material. This paper describes an ongoing research project of the Cotton Defoliation Work Group and includes data collected from 16 growing regions over a three year period (1992 - 1994). The objective of this beltwide project is to develop effective, practical harvest aid recommendations that contribute to harvest efficiency and high quality fiber, especially by evaluating performance of standard defoliation treatments on a uniform basis and relating this performance to biotic and environmental factors. Analysis of lint quality data revealed little differences among harvest aid treatments when recommended production practices are followed. Most of the fiber quality differences between the untreated check and the harvest aid treatments were of little practical significance. Harvest aids can reduce trash, reduce micronaire and improve color. Harvest aids did not increase white specks or neps, reduce strength, length or uniformity. Even though differences in defoliation efficacy are measured, ginning and lint cleaning tend to normalize differences in trash content.