Ethiopian Somali goats are well accustomed to their hot and dry environment. Which physiological and behavioural mechanisms are used by the goats, which enables them to survive and produce milk during repeated periods of dehydration? Seven does (W4) were given water every fourth day and seven does were watered once daily (W1) during 32 days in total. The goats were kept in an enclosure during the night and on pasture during day-time. Rectal temperature was measured at 0800 h and 1715 h. Blood and milk samples were taken once daily. Plasma vasopressin concentration was analysed by radioimmunoassay. Water intake of W4 was 4877 ± 189 ml after the first 4 days of water deprivation, but decreased with each cycle and at the end of the experiment the goats drank only 3422 ± 191 ml of water when given access to water. In comparison the W1 goats drank in total 7588 ± 386 during 4 days (P < 0.001). In W4 goats the plasma osmolality dropped more every time the goats had drunk after water deprivation. This indicates that the goats started to store water in the extracellular fluid. Thus the plasma osmolality increased to 336 ± 2 mosm/kg at the end of the first period but only to 306 ± 2 mosm/L (P < 0.001) at the end of the last cycle. The corresponding vasopressin concentrations were 10.0 ± 0.8 and 4.4 ± 0.6 pmol/L (P < 0.001). The mean afternoon rectal temperature was 3.5 ordm;C higher than in the morning in both groups. Milk production was 22 % lower in W4 compared with W1 in all periods. With repeated days of water deprivation, the W4 goats spent less time in the sun, grazed shorter time and ate more watery plants. The results suggest that these goats economized on water by diurnal variations of rectal temperature, storing water in the extracellular fluid, by changing behaviour and by decreasing milk production.