The measurement of somatic cell counts (SCC) is used in the UK to detect the presence of sub-clinical mastitis in dairy cattle (Mrode & Swanson, 1996). Many studies have investigated the relationship between farm hygiene and management factors on the herd average SCC (from the bulk milk tank) and have shown that factors such as milking parlour hygiene, the use of straw-yard systems, cleanliness of the lying area and mastitis treatment strategies affect SCC (e.g. Barkema et al., 1999; Peeler et al., 2000). The organic status of the farm may also affect SCC. The principles of livestock farming are that animal health should be promoted through good animal care and management, and this is particularly emphasised for organic systems. Organic standards discourage the general prophylactic use of chemically synthesised allopathic veterinary medicines, such as antibiotics. Use of alternative remedies, such as homeopathy, is encouraged for the treatment of disease. Antibiotics can be used in acute cases, such as for clinical mastitis, but the withdrawal period for sale of milk is longer on organic farms than for non-organic farms. There is concern that these regulations may have a negative impact on animal health and welfare, particularly if alternative health treatments are ineffectual. The aim of this study was to determine whether organic status and other farm management practices affect SCC in organic and non-organic farms.