1. From Streptococcus faecalis a third novel phosphoglucolipid was isolated. It contained D-glucose, glycerol, acyl groups and phosphorus in a molar ratio of approx. 2 : 3 : 4 : 2. 2. The structure was shown to be 3(1)-O-[6 inches-(sn-glycerol-1-phosphoryl), 6 foot-(1,2 diacyl-sn-glycerol-3-phosphoryl)-2 foot-O-(alpha-D-glucopyranosyl)-alpha-D-glucopyranosyl]-1(3),2-diacylglycerol. The novel lipid is related to the earlier described phosphatidyl and glycerophosphoryl kojibiosyl diacylglycerol from Streptococcus faecalis by combininb their substituents in its structure. 3. The structure of the deacylated core was accomplished by analyses of the breakdown products obtained on Smith degradation and strong alkaline hydrolysis. The location of the acyl groups was achieved by degradation of the intact lipid with 60% HF (w/v) which resulted in the formation of inorganic phosphate, glycerol, diacylglycerol and diglucosyl diacylglycerol. The sn-glycerol-1-phosphoryl and 3-sn-phosphatidyl substituents were located by hydrolysis of the lipid with 98% acetic acid (v/v) and subsequent analysis of the resultant phosphatidyl diglucosyl diacylglycerol. 4. The composition and positional distribution of the constituent fatty acids at the two diacylglycerol portions was studied by combination of chemical and enzymatic degradations. The fatty acids are the same as with the other polar lipids of S. faecalis, they are present in nearly the same proportions and display the same non-random distribution pattern. 5. A possible relationship between sn-glycerol 1-phosphate containing phosphoglucolipids and lipoteichoic acid will be discussed.