Nutritionally balanced heterokaryons of the naturally diploid, asexual yeast, Candida albicans are produced by fusing protoplasts of complementing auxotrophic strains. Spontaneous unidirectional internuclear transfers of an intact gene linkage group in established heterokaryons is demonstrated. Evidence is presented that a transfer event (i) typically involves a single chromosome which is added to the resident homologues of a recipient nucleus, (ii) can occur equally well in either direction between complementing nuclei and (iii) may encourage gene conversion at transferred loci in the recipient nucleus. The bearing of these findings on application of protoplast fusion to parasexual genetic analysis of C. albicans is discussed.