Highly purified equine herpesvirus type 1 (EHV-1) and herpes simplex virus type 1 (HSV-1) were observed by electron microscopy in various stages of disintegration. Under the conditions used, envelopes of virions usually were fragmented, and virus capsids collapsed in situ into flattened sheets of capsomeres. A matrix of intercapsomeric fibrils was observed. Evidence suggesting that the capsid hexamer has threefold structural symmetry is presented.