Darb Al-Arbain is a virgin area and represents the southern boundary of the Egyptian oasis depression. It considers one of the most promising areas for agricultural expansion in Egypt. This study aimed to setup a preliminary data on some health indices including clinical, haematological, hormonal and metabolic picture in desert (Barki) and Nile valley (Rahmani and Ossimi) sheep, which were recently transported with their owners to this newly reclaimed area. Also, to correlate between these indices and the temperature humidity index (THI) as a trial to evaluate the effect of heat stress on the health indices of these sheep. To nullify the effect of age throughout the study period (6 months), this work was designed to select 3 groups of male lambs (15 each; average 7 months and around 24 kg). Each group represented two months of the study period, so that the three groups represented a cycle of 6 consecutive months began by February (basal data) to July (intensified dry summer stress). Each group included three subgroups of Rahmani, Ossimi and Barki lambs (5/breed). Clinical, haematological and biochemical investigations were carried out monthly throughout 6 months study period. The average of maximum ambient temperatures at the end of July was 154.7% higher and the relative humidity was116.8 lower than the basal thermoneutral data. The effect of breed under the changes of THI was significant for rectal temperature, respiratory rate, PCV, potassium and cortisol. The patterns of estimated parameters were insignificantly fluctuated in Barki and Ossimi sheep except the significant elevation of rectal temperature and respiratory rate (at THI above 90). In Rahmani sheep, the magnitude of rectal temperature and respiratory rate (at THI 85 and 88 respectively) preceded those in other breeds. On the other hand the values of RBC, Hb, PCV, plasma total protein, albumin, K, T₃ were decreased and Na and cortisol values were increased in Rahmani sheep when THI reached 92. Correlation coefficient showed that respiration rate was highly correlated with increasing THI (r=0.738, P=0.0005), whereas rectal temperature was less responsive to THI (r = 0.561, P=0.015). It was noticed also that THI was negatively correlated with RBC, PCV, total protein, albumin, potassium, T₃, T₄ and positively correlated with Na. In conclusion, the hot arid and drought desert environment did not affect health indices in Barki and Ossimi sheep inhabiting Darb Al-Arbain area. The measured values were within the normal physiological ranges reported for sheep. In despite, the changes in clinical and biochemical indices showed that health of Rahmani breed was at risk only when THI was above 85 and not at 81 as reported for temperate breeds. From these results, this study recommends to establish suitable new THI categories for native breeds reared under tropical environment.