Proper timing of harvest-aid treatments requires a reliable estimate of crop maturity. Current guidelines for application of defoliants and desiccants (i.e., percent open bolls) are qualitative in nature and usually somewhat conservative. During 1990 and 1991, field trials were conducted in four states to quantify the effects of crop termination at various maturity stages on yield and quality. Results were used to develop objective crop termination guidelines using simple plant monitoring techniques based on nodes above the uppermost cracked boll (NACB). Crop termination with defoliants at < 3 NACB resulted in essentially no yield or micronaire reductions. In contrast, rapid termination with chemical desiccants should be delayed until 2 NACB. With information regarding the number of fruiting branches that contribute to yield, percentage of yield contributed by each fruiting branch and location of the uppermost first position cracked boll, potential yield losses associated with crop termination at a predetermined NACB can be predicted. Use of the NACB method to time harvest-aid applications will be most effective in fields that are uniform with regard to crop emergence, fruiting initiation and fruit retention. In non-uniform crops, other guidelines should be used in conjunction with NACB to insure proper timing of harvest-aid treatments.