This study was undertaken to determine aetiology and prevalence of subclinical mastitis in manually and mechanically milked animals in the north of Palestine. Milk samples from animals with bacterial infection of the mammary gland showed significantly higher somatic cell count (SCC) than did the corresponding milk from healthy animals, which (1,420±100 X103 cells/ml; vs. 330±35 XIO3 cells/ml; 1650±155 XIO3 cells/ml vs. 490±40 XIO3 cells/ml; 520±50 XIO3 cells/ml vs. 140±25 X10J cells/ml) for ewes, goats and cows, respectively. The prevalence of bacterial isolation of the milk from goats (n = 25), sheep (n = 40) and cows (n=220) from several major herds was determined. Culturing for bacteria revealed that 52 %, 72.5% and  59.1% of tested  goats,  sheep and  cows  had  subclinical  mastitis,