A procedure to isolate large quantities of capsular polysaccharides (CPS) from culture supernatants as well as bacterial cells of gram-negative and gram-positive bacteria using base extraction is described. The procedure is simple, rapid, reproducible and applicable to a variety of bacterial species. The method also yields novel CPS characterized by their lack of covalent attachment to extraneous peptidoglycan. Vaccines and methods of immunization against bacterial infection using the CPS obtained by the process of the invention are also disclosed. A group B streptococcal capsular polysaccharide produced comprises type Ia CPS having K av approximately of the range 0.010 - 0.005 M w approximately of the range 318 - 311 (kg/mol) M w /M n approximately of the range 1.35 -1.31； type Ib CPS having K av approximately of the range 0.191 - 0.150 M w approximately of the range 218 - 170 (kg/mol) M w /M n approximately of the range 1.61 - 1.20； type II CPS having K av approximately of the range 0.152 - 0.115 M w approximately of the range 289-246 (kg/mol) M w /M n approximately of the range 1.46； type III CPS having K av approximately of the range 0.343 - 0.268 M w approximately of the range 108 - 104 (kg/mol) M w /M n approximately of the range 1.24 - 1.22； type V CPS having K av approximately of the range 0.257 - 0.156 M w approximately of the range 179 - 92 (kg/mol) M w /M n approximately of the range 1.28 - 1.15.
