Interspecific somatic hybridization was performed between embryogenic callus protoplasts of Asparagus officinalis cv. Mary Washington and callus protoplasts of A. macowanii by electrofusion. By utilizing iodoacetamide (IOA) inactivation treatment for A. officianlis protoplasts and the difference of cell division capacity between the two species, one callus line, which had an ability to produce somatic embryos, was selected as a putative hybrid. Normal germination of the somatic embryos was induced only when they were exposed to a period of cold treatment (14 days at 4°C). However, the regenerated plants showed intermediate but abnormal morphological characters in vitro as well as after transfer to soil. The hybrid nature of the plants derived from this callus was confirmed by isozyme, nuclear rDNA and random amplified polymorphic DNA (RAPD) analyses and counting the chromosome number.