Antisense compositions targeted against an mRNA sequence coding for a selected protein, at a region having its 5′ end from 1 to about 25 base pairs downstream of a normal splice acceptor junction in the preprocessed mRNA, are disclosed. The antisense compound is RNase-inactive, and is preferably a phosphorodiamidate-linked morpholino oligonucleotide. Such targeting is effective to inhibit natural mRNA splice processing, produce splice variant mRNAs, and inhibit normal expression of the protein.