We investigated effects of subclinical intramammary infection (IMI) on milk somatic cell count (SCC) and milk composition in udder halves of dairy goats. A total of 35 mixed-age Alpine does (70 udder halves; approximately 55 kg body weight) were rotationally grazed on a mixture of vegetative forages (wheat/berseem clover, sudan grass and cowpeas). Milk samples for bacterial analysis and SCC were collected monthly from both halves from April to September, 2001. Across stages of lactation, 19–31% of udder halves became infected. The prevalence of IMI exhibited quadratic patterns through multi-peaked responses within each stage of lactation. Higher rates of IMI were observed during the early stage of lactation (19% in May) and in the late stage of lactation (31% in September). Coagulase negative Staphylococcus (CNS, 43·7%), Staph. aureus (35·4%), and Pseudomonas aeruginosa (12·4%) were the most prevalent pathogens. Within single-strain IMI, log SCC (6·24) was lower (P<0·01) for CNS than those derived from IMI by Staph. aureus (6·49), Ps. aeruginosa (6·53) or Serratia spp. (6·90). Infected udder halves had a higher average SCC (4761 v. 2259×103 cells/ml; P<0·01) than uninfected halves, but uninfected halves often had similar levels of SCC to infected halves. Daily average milk production was not significantly different between infected and non-infected goats and the relationship between IMI and SCC was not always correlated. Effective mastitis screening requires bacteriological culture since SCC was not highly correlated.