We have compared mitochondrial transcripts from yeast Saccharomyces cerevisiae strain D273-10B grown in the presence of 2% galactose (non-repressed cells) or 15% glucose (glucose-repressed cells). The ethidium-bromide-stained electrophoretic pattern of mitochondrial RNAs from glucose-repressed cells shows a clear decrease of tRNAs. In addition, some RNA bands appear to be specific for a single growth condition. To identify these RNA species we have performed hybridization experiments with 32P-labelled mitochondrial DNA from petite mutant cells. The mitochondrial repeat units of the mutants retained only one of the following genes: oxi1, oxi2, oxi3, oli2, cob and oli1. Unchanged amounts of oxi2 and oli2 transcripts and reduced concentrations of oli1 and oxi1 putative mRNAs are present in glucose-repressed cells. In the same growth condition we observe a decreased processing of a precursor RNA species from the split cob gene and reduced amounts of transcripts corresponding to the first, second and fifth intron of the split oxi3 gene. The oxi3 first and second introns, whose transcripts are the most variable, include long open reading frames in their nucleotide sequence, but at present it is not known whether the corresponding RNA species have a functional role. Our results show that their concentrations are related to the growth condition.