Somatic cell count (SCC) is generally regarded as an indicator of udder health. A cut-off value of 100×103 cells/ml is currently used in Germany to differentiate between normal and abnormal secretion of quarters. In addition to SCC, differential cell counts (DCC) can be applied for a more detailed analysis of the udder health status. The aim of this study was to differentiate somatic cells in foremilk samples of udder quarters classified as normal secreting by SCC <100×103 cells/ml. Twenty cows were selected and 72 normal secreting udder quarters were compared with a control group of six diseased quarters (SCC >100×103 cells/ml). In two severely diseased quarters of the control group (SCC of 967×103 cells/ml and 1824×103 cells/ml) Escherichia coli and Staphylococcus aureus were detected. DCC patterns of milk samples (n=25) with very low SCC values of ⩽6·25×103 cells/ml revealed high lymphocyte proportions of up to 92%. Milk cell populations in samples (n=41) with SCC values of (>6·25 to ⩽25)×103 cells/ml were also dominated by lymphocytes (mean value 47%), whereas DCC patterns of milk from udder quarters (n=6) with SCC values (>25 to ⩽100)×103 cells/ml changed. While in samples (n=3) with SCC values of (27–33)×103 cells/ml macrophages were predominant (35–40%), three milk samples with (43–45)×103 cells/ml indicated already inflammatory reactions based on the predominance of polymorphonuclear leucocytes (PMN) (54–63%). In milk samples of diseased quarters PMN were categorically found as dominant cell population with proportions of ⩾65%. Macrophages were the second predominant cell population in almost all samples tested in relationship to lymphocytes and PMN. To our knowledge, this is the first study evaluating cell populations in low SCC milk in detail. Udder quarters classified as normal secreting by SCC <100×103 cells/ml revealed already inflammatory processes based on DCC.