ChaperoneTM is a new plant growth regulator that has been marketed as a plant protein enhancer for increased lint yields but the evidence for this has been lacking. Field and growth chamber studies were conducted in 2002 to 2006 to quantify the effect of foliar applications of Chaperone on protein and endotoxin levels of cotton (Gossypium hirsutum L.) leaves and squares, and the subsequent effect on bollworm mortality and yield. Preliminary studies revealed that the optimum rate and timing of Chaperone was 350 ml/ha applied once at the start of flowering. In field studies, Chaperone at 350 ml/ha applied at first flower compared to the untreated control increased yield by an average of 8%. In addition, one week after application, there was an increase in petiole nitrate levels by 12%, proteins in the leaves by 4% and in the squares by 13%. In addition, there was improved expression of the Bt endotoxin protein in the squares by 6%. The increased endotoxin protein resulted in 10% higher mortality of bollworms feeding on treated plants compared to untreated leaves 10 days after application. These results were confirmed in growth room studies. The results showed that foliar applications of Chaperone may be a viable means for increasing lint yields in cotton through the enhancement of plant protein levels. Furthermore, the enhanced protein status contributes to improved late-season endotoxin levels in the squares, which contributes to increased mortality of bollworms feeding on the treated plants.