Capsids of herpes simplex virus (HSV) types 1 and 2 contain seven polypeptides ranging in molecular weight from 154,000 to 12,000 (termed NC-1 through NC-7 in order of descending molecular weight). Antibodies prepared to HSV-1 capsid polypeptides isolated from sodium dodecyl sulfate-polyacrylamide gels reacted in an immunofluorescence assay against HSV-1-infected KB cells. Three of the antibodies (anti-NC-1, anti-NC-2, and anti-NC-3,4) also reacted with HSV-2-infected cells. Tryptic peptide analysis showed that each of the HSV-1 capsid polypeptides had a unique methionine peptide profile, and none appeared to be derived from the major capsid polypeptide. Comparative peptide analysis of HSV-1 and HSV-2 showed that one polypeptide (NC-7, 12,000 molecular weight) had an identical methionine peptide profile and a very similar arginine peptide profile in both virus types. The arginine peptide profile of NC-7 of HSV-1 was very different from the arginine profile of KB histone H4. Although there were certain intertypic similarities in the methionine peptide profiles of the other capsid components especially in NC-1 (the major capsid protein), there was no case where the tryptic peptides were identical in the two virus types.