Three hundred fifty one (195 local zebu and 156 Holstein x Local Zebu) lactating cows ofrnsmallholder private farms in Bahir Dar milk shed were examined from September, 2003 tornMarch, 2004 to determine mastitis prevalence, isolate pathogens involved, evaluate thernantibiotic susceptibility profiles and to evaluate somatic cell count in identifyingrnintramammary infections. Clinical prevalence was determined through examination ofrnabnormalities of milk, udder or cow. California mastitis test (CMT) and culture were used forrnsubclinical mastitis determination. Agar disc diffusion was used for antibiotic susceptibilityrntest. Somatic cell count was conducted following standard procedures described inrnInternational Dairy Federation for enumeration of cells with direct Microscopic method.rnClinical prevalence at cow level was 3.9% in crossbreds and none in local zebu breeds.rnSubclinical mastitis at cow level based on CMT was high (34.4%) in crossbreds compared tornindigenous zebu (17.9%) (p < 0.05). Quarter subclinical prevalence based on CMT wasrn17.90% and 4.95% for crossbreds and local zebu, respectively. Among potential risk factorsrnconsidered, stage of lactation, parity and breed were found to affect the occurrence of mastitisrnsignificantly (p < 0.05). The pathogens isolated from mastitic milk were coagulase negativernstaphylococci (CNS), S. aureus, Str. agalactiae, Str. dysgalactiae, Str. uberis, Micrococcusrnspecies, C. bovis, A. pyogens, B. cereus, and S. intermedius. Among these, the most frequentrnisolates were CNS (49.6% of the total isolates), S. aureus (17.9%), Str. agalactiae (8.2%) andrnStr. dysgalactiae (6.7%).rnSeven antibiotics including sulfisoxazole, tetracycline, erythromycin, oxacillin,rnchloramphenicol, clindamycin, and streptomycin were tested on 81 isolates. Except forrnstreptomycin, all isolates were sensitive to all antibiotics. All isolates were most sensitive tornsulfisoxazole. Staphylococcus aureus was susceptible to all drugs except streptomycin.rnStaphylococcus aureus was 91.7% susceptible to oxacillin, however, CNS were lessrnsusceptible (68.2%) in vitro.rnTo evaluate somatic cell count (SCC) in identifying intramamary infection for crossbreds, 10rncutoff points between 100000 cells/ ml and 300000 cells/ml were evaluated for theirrnsensitivity and specificity in comparison with cultural results. Similarly, cutoff points betweenrn80000 cell/ml and 250000 cell/ml were taken for local zebu breeds. The sensitivity forrnviiirncrossbreds range from 79.16 % (at 300000 cells/ml cutoff point) to 95.80 % (at 100000 cells/rnml) and similarly specificity from 80.28% to 45.52%. For local zebu breeds in the same order,rnsensitivity range from 58.82% to 88.23% and specificity from 45.82% to 85.15%. Tornestablish threshold level this study was a first attempt in Ethiopia and to use SCC as arndiagnostic tool on a national scale further study need to be conducted with improved culturalrntechnique and automatic cell counters. Cross breed cows had high SCC compared to localrnzebu cows. The SCC was significantly (p