Foremilk and strippings were obtained from 20 cows at the morning and evening milkings where the milking intervals were 14 h and 10 h. Infection status was determined by bacteriological analysis. Conductivity of foremilk and strippings was determined. Cows then were switched to 12 h milking interval, and conductance of foremilk and strippings from both milkings was determined. Conductance of foremilk samples increased after longer milking interval. Accuracy in detecting infections by primary pathogens via conductivity of foremilk was also greater following the long interval. Conductivity of foremilk from morning and evening milkings were, however, similar when the milking interval was even. Conductivity of strippings was affected less by milking interval. Conductance determination on quarter samples from 28 cows on both a whole and fat-free basis indicated an inhibitory effect of milk fat on conductivity. Conductivity of skimmed strippings samples was greater than that of skimmed foremilk samples, indicating higher electrolyte in strippings, and may explain why conductivity of strippings is not significantly lower than of foremilk in spite of the higher fat content in the former