Two field experiments were conducted during the two successive early and late summer seasons of 2002 and 2003 at Kaha Vegetable Research Station (Qalubia Governorate) on tomato plants (Lycopersicon esculentum, Mill.) cv. Super Strain B to study the effects of Biomagic^® (7.5 g/l),  Baker's Yeast solution – Yeast (foliar), Yeast (soil) and Yeast (foliar+soil) - (10×10⁹ cells /l), Acadian Seaplants^® (1 l/ feddan), Foliafeed (D)^® (0.625 g/ l), the trial (experimental) compound fertilizer (5 g/ l), putrescine (1 mg/l), silicon's powder, unadulterated sand (1 g/l)  as well as sodium meta silicate (1 g/l) under two different periods of early and late summer seasons (heat stress conditions) on the different vegetative growth characters, flowering as well as yield and its components. This work aimed to rise the ability of this cultivar to tolerate the hard conditions of heat stress, prevailing in this period of year (May, June and July), which causes a severe drop in the productivity.       The obtained results indicated that, all applied treatments significantly increased the most of the studied vegetative growth characters. The greatest values of the two successive early summer seasons were obtained by treating plants with Yeast (foliar+soil) as well as Biomagic^®. Foliar application of Biomagic^®, siliconיs powder as well as compound fertilizer resulted significant decreases in the number of days required for flowering 50 % of plants in the first season. In addition, the highest value in the early tomato yield (ton/ feddan) were recorded by using Biomagic^® followed by siliconיs powder treatments. Also, the applied treatments significantly decreased the values of the non-marketable tomato yield. All different treatments showed significant increases in the average fruit weights, total sugars in leaves and fruits, essential amino acids, non-essential amino acids, total amino acids and total proteins % of tomato leaves with some exceptions when compared to the control untreated plants.       Under the heat stress conditions (two late summer seasons), all applied treatments recorded higher values of different vegetative growth characters (plant height, number of branches and leaves) as compared to the two early summer seasons. No significant decrease on the number of days required for flowering of 50 % of plants under conditions of heat stress were recorded. Number of clusters/ plant were increased specially at 70 days after transplanting (D. A. T.). On the other hand, fruit set percentage as well as early, marketable and total tomato yield were decreased whereas, non-marketable yield increased as a result of heat stress conditions. The best treatments under this condition were application of putrescine, Foliafeed (D)^®, Biomagic^® as well as Yeast (foliar+soil) which increased most of these parameters. All different treatments showed significant increases in the average of fruit weights, total sugars, essential amino acids, non-essential amino acids, total amino acids as well as total protein % of tomato leaves with some exceptions as compared with the early summer season and when compared to the control (untreated plants).