Protoplast fusion using polyethylene glycol (PEG) was conducted to combine Citrus sinensis (L.) Osbeck cv. 'Hamlin' sweet orange protoplasts, isolated from nucellus-derived embryogenic callus with Atalantia ceylanica (Arn.) Oliv, leaf protoplasts. Five plants regenerated from independent fusion events following protoplast culture were identified as intergeneric allotetraploid somatic hybrids of 'Hamlin' sweet orange and A. ceylanica, and confirmed by isozyme analysis and chromosome number determination in root tip cells (2n=4x=36). Two different types of leaf morphology were observed among the hybrids (normal and narrow), although no differences in chromosome number nor isozyme banding patterns were observed. This is the first report of the production of hybrid plants between these sexually incompatible genera.