Opsonic and antibody responses to pneumococcal polysaccharide types 6A, 19F and 23F were evaluated before and after vaccination with a 14-valent pneumococcal vaccine in 25 patients splenectomized due to trauma, non-malignant or malignant disease and in 8 non-splenectomized patients with malignant disease. In approximately 50% of the tests, a 2-fold or greater increase in antibody concentrations and a significantly enhanced opsonization of pneumococci was found. A close correlation between antibody increase an enhancement of opsonization was demonstrated. 93% of paired samples with postimmunization antibody increase above 150 ELISA units showed significantly enhanced opsonization. Increased postvaccination opsonic activity and antibody levels were infrequently accompanied by increased granulocyte chemotactic activity of the serum. No significant difference in antibody and opsonic response to vaccination was found between the groups of patients, except for patients with Hodgkin's disease receiving chemotherapy, who had a reduced immunization response. Prevaccination antibody concentration, type of antigen or age of the patients did not influence the outcome of vaccination.