The haemophilus vaccines are made of the type b capsular polysaccharide of haemophilus influenzae, polyribosylribitol phosphate (PRP), which is responsive of pathogenic power. However the responsiveness of children to PRP vaccine was found to be very poor in infants. The concept of conjugating carbohydrate with a carrier protein increasing immunogenicity of the PRP led to 4 PRP--protein conjugate vaccines: PRP-diphtheria toxoid conjugated vaccine (PRP-D), outer-membrane protein of Neisseria meningitidis conjugated (PRP-OMP), cross-reacting mutant diphtheria protein (PRP-HbOC) and tetanus-Toxoid conjugated vaccine (PRP-T). The antibody response to PRP is enhanced and a good booster response is obtained in infants as soon as two months of age. However the 4 vaccines differ markedly in ability to stimulate antibody production. PRP-D is less immunogenic and must be given in children older than 12 months. Antibodies are significantly higher after 3 injections of PRP-T or PRC-HbOC than PRP-OMP. Only PRP-OMP produces a clinically pertinent elevation of antibodies after 2 injections. The coadministration of PRP-OMP, PRP HbOC, PRP-T with diphtheria-tetanus-pertussis vaccines does not alter the antibody PRP response. The polio antibodies are lower if injectable polio vaccine is mixed with PRP-OMP, but the level is the same with PRP-T vaccine. The others antibodies (D, T, Coq), are at same levels. The field trials have shown a high efficacy of all those 4 vaccines. However PRP-D vaccine gave less good result in infants before 6 months. The safety of these vaccines is good and not altered by combination with investigation by diphtheria-tetanus-pertussis vaccines.(ABSTRACT TRUNCATED AT 250 WORDS)