Adaptation of small ruminants (sheep and goats) to semi-arid conditions was studied. Blood samples were collected from five adult Ossimi ewes and five Zaraibi goats at weekly intervals for 8 weeks during three seasons; winter (December - January), summer (July - August) and spring (March - April). Water was available ad libitum. During August, the responses of the animals to severe heat stress of direct solar radiation were recorded, Water was not available during the exposure period (from 12.00 noon to 3.00 p.m). The responses to salt in drinking water (NaCI 13.0 g/I distilled water) and to water deprivation for a period of 48 hours were Studied. The mean values of Nat (mg/100 ml) in blood plasma were significantly different among Seasons. The values of Nat concentration tended to decline gradually from winter (351.5 and 370.2) to spring (211.5 and 207.0) to summer (125.9 and 122.6) in both sheep and goats, respectively, which means that higher ambient temperature might be one of the reasons of this decline. The concentrations of Na⁺⁺ in blood plasma in both stressed sheep and goats were higher (561.7 and 578.6) than those which were given saline water (430.1 and 448.6) and those under water deprivation (465.7 and 505.7), respectively. Potassium concentration in blood plasma (mg/100 ml) showed opposite trend, the higher values were recorded during summer (19.2 and 19.1) and lower values during spring (13.8 and 13.9) in both sheep and goats, respectively. When the two species were compared during periods of water deprivation (WD) and water salinity (WS), goats showed higher concentration of Nat accompanied by Lower concentration of K⁺ than the values in sheep. However, during heat stress period, goats had higher values in both Na⁺ and K⁺  concentrations than sheep. Aldosterone concentration varied between seasons in both sheep and goats, the higher values were recorded during the hot summer season. During heat stress, plasma aldosterone in goats was double than that in sheep, while opposite trend to heat stress occurred during (WD) and (WS) where sheep recorded higher values than goats.