The somatic cells of cow's milk were separated by filtering through nitrocellulose membrane filters (Synpor), pore size 2 to 5 micron. An indole reagent was added to the membrane filters with trapped cells, the mixture was warmed in boiling water bath for 20 min., then cooled, centrifuged (3500 X g, 15 min.), and optical density was measured at 490 nm. The relation 8 micrograms = 1 million cells was used for the conversion of DNA content in sample to the counts of cells. The average variation coefficient of the determination was 4.7% and the coefficient of correlation between the indole DNA filter method and direct microscopy on membrane filters was r = 0.997. Using the indole DNA filter method, the counts of somatic cells can be estimated from milk samples kept frozen or from filters with retained cells kept at 4 degrees C, or (for a short time--3 days) at 25 degrees C. The estimation is not distorted when the milk samples are stabilized with K2Cr2O7 or a mixture of K2Cr2O7 and HgCl2, if they are kept at 4 degrees C for eight days.