Interspecific hybrids of various Epilobium species have been produced in order to analyse plastid inheritance using restriction fragment polymorphisms of plastid DNA as markers. This analysis reveals that interspecific hybrids exhibit only the fragment pattern of the maternal plastome. Southern hybridization experiments using cloned species-specific plastid DNA fragments as markers confirm the maternal type of plastid inheritance in Epilobium, while providing at least a tenfold increase of sensitivity to detect restriction polymorphisms. Within the limit of detection even young seedlings contain no plastid DNA from the paternal parent. However, investigations of plastomes of large populations have provided evidence that a very low frequency of paternal plastid transmission can occur. Thus, the mechanism which ensures the elimination of paternal plastids is not 100% efficient. This suggestion is also supported by intraspecific reciprocal crosses between plants carrying mutant white and normal green plastids. While the offspring usually exhibit the maternal plastid type, a few cases indicate an apparent paternal plastid transmission.