Mucin clots from cattle submaxillary glands were lyophilized as sodium salts with retention of the viscosity of the extracts and of solubility in water. The viscosity was 25.8 cP in 1% aqueous solution and 4.5 cP in 1% phosphate buffer of pH 7.4 and ionic strength 0.1. The specific rotation was [ α] D 25 = −23.2 ° (0.87 per cent in water). The mucin contained about 13 per cent sialic acid, 11 per cent hexosamine (8 per cent galactosamine and 3 per cent glucosamine as the acetyl derivatives) and 75 per cent protein. The molar ratio of galactosamine to sialic acid was unity. The mucin showed four peaks when subjected to electrophoresis at pH 10 in a phosphate buffer of ionic strength 0.1. The average mobilities were −7.2, −8.0, −10.3 and −11.3 × 10 −5 cm 2/sec per V, respectively, at pH 10. Three components were evident at pH 7.4 and 8.0, and only two at pH 6. The major component had a mobility of −6.3 × 10 −5 at pH 7.4. Two ultracentrifugal components of 2.1 and 2.5 S were evident at pH 7.4. At pH 10, a small more rapidly moving 5.0 S component was also present.