Herpes simplex virus type 1 (HSV-1) encodes five immediate-early (IE) genes, at least three of which are involved in the regulation of gene expression. Gene IE-1 is one of the few HSV-1 genes whose pre-mRNAs are spliced; the IE-1 pre-mRNA contains two introns, the second of which contains an in-frame stop codon which would terminate IE-1 translation if the intron were not excised. Previous work has shown that plasmids which have been constructed so as to express only the first two exons of Vmw110 can inhibit gene expression in transfection assays, whereas the normal intact protein is an activator of gene expression. In this paper we show that this predicted truncated Vmw110 protein is expressed during normal HSV-1 infection, and that it must be translated from IE-1 pre-mRNAs which retain the in-frame stop codon in the second intron. This truncated product is produced in amounts which depend upon the cell type infected. The possible consequences of these observations are discussed.