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SummaryPotato plants obtained by symmetric and asymmetric protoplast fusion experiments with Solanum tuberosum and Solanum circaeifolium were compared and their potential use for plant breeding was investigated. For asymmetric hybridisation wild species tissue was irradiated with X-rays. Irradiation enhanced regeneration frequency. RFLP analysis showed that both techniques gave approx. 95% hybrids among the regenerates, Asymmetric protoplast fusion gave 22% regenerates with a ploidy level between 2x and 4x or 4x and 6x. None of the regenerates obtained from symmetric fusion had these ploidy levels.The tetraploid hybrids showed good male and female fertility. Male fertility was highest for the eutetraploid regenerates. With increasing asymmetry and with increasing ploidy level fertility decreased. Berry induction and seed production were observed for the eutetraploid and, to a lesser degree, for the hypotetraploid and hypohexaploid hybrids.