The physiological range and the potential of diagnostic thresholds for the somatic cell count (SCC; [log₁₀/ml]) during the colostral phase (1^st to 7^th day postpartum (p.p.)) were investigated. 370 quarters of 97 Holstein-Friesian cows in Northern Germany were sampled at the 1^st (F1) and 2^nd (F2) week p.p. and examined cytobacteriologically. The higher the SCC value of a quarter in F1, the lower was the possibility of returning to a level <4.67 log₁₀/ml in F2. After categorisation of udder quarter health in F2, the SCC of F1 was studied retrospectively. For the first 2 days p.p., colostrum SCC was inadequate for mastitis diagnosis since there was no significant difference between healthy and diseased quarters. However, from day 3 p.p. on, there was a significant difference (p<0.02) with a mean SCC of 4.61±0.56 log₁₀/ml in healthy quarters. The threshold for healthy quarters was 5.20 log₁₀/ml colostrum (160000 cells/ml) with a specificity of 92%, a sensitivity of 20% and a least probability of misclassification of 18%. Thus, colostrum can be a useful additional tool in early lactation mastitis diagnosis when sampled at day 3 p.p. at the earliest, and with a threshold of 160000 cells/ml colostrum for interpretation.