Abstract: A medically important and useful conjugate comprising pertussis toxin (PT), or another antigen having similar physico-chemical properties, as the carrier protein component, coupled to a neutral or non-charged saccharide, particularly, the capsular polysaccharide of Streptococcus pneumoniae type 14 (Pn14), for use as an effective, non-toxic, and highly immunogenic vaccine is described. The invention is directed to a novel synthetic scheme wherein PT and like proteins, and a derivative of Pn14, and the like, were coupled at acidic pH via carbodiimide-mediated condensation to produce an immunogenic conjugate. The coupling procedure yielded a Pn14-PT conjugate in which the PT component was rendered non-toxic and both the PT and Pn14 components were immunogenic, as determined by the production of protective levels of both type-specific and neutralizing antibodies in mammals.