Four field experiments were conducted in late summer seasons of 1998 and 1999 to study different responses of some vegetable crops, i.e. tomato cv. Castel Rock (first exp.), sweet pepper cv. California Wander (second exp.), snap bean cv. Bronco (third exp.) and cowpea cv. Creem-7 (fourth exp.) grown in late summer season to induce thermotolerance responses  (improvement of fruiting and yield) by using yeast preparation (Y₁ & Y₂) (25 ml/L & 50 ml/L), chelated micronutrients (CME) (1 ml / L), iodo-benzoic-salicylic acid (IBS) (0.2 gm/L) and royal jelly (RJ) (10 ppm) three times spraying on tomato. Also, Y₁, Y₂, IBS and ATP (50 ppm), three times spraying on pepper, snap bean and cowpea in other experiments. The results could be summarized as follows:-      Different vegetable crops differed in their morphological and nutritional behavior as well as fruiting and yield as a result of application the same treatments under the same stress condition.      In first exp., with tomato, IBS and RJ were the best treatments for improving nutrients content, fruiting and yield. RJ gave rise to the best vegetative growth. IBS increased yield by 142.3% and RJ by 125.0% (mean of two season) above control. Also, tomato relative to other crops was of the highest response to the same treatment based on RY value.      Sweet pepper (second exp.) followed snap bean in its response for the same treatment (based on RY value). ATP treatment was the best for growth, nutritional case, fruiting and yield (161.2% of control).      Snap bean followed tomato in its responses. Yeast preparation (Y₂) 50 ml/L was the best treatment for growth, most chemical contents and yield (186.0% of control).      Cowpea was relatively the least thermosensitive crop (at the same basis). ATP was the best treatment for growth, whereas IBS was the best for nutrients content, fruiting and dry seed yield, it increased seed yield by 30.0% above control.      Present work allowed to own new specific techniques and promising growth and fruiting substances as yeast preparation (a natural growth stimulator rich in auxins, GA₃, cytokinins and several essential bioconstituents), IBS as a new synthetic growth inhibitor of great benefits specially during stress condition and new balanced chelated microelements combination (CME) with new specialized technique.      Successfully application of such new substances on different vegetable crops in critical season to induce thermotolerability and considerably increase their fruiting and yield.