Over 80% of the maxicircle and numerous minicircles of Trypanosoma brucei kinetoplast DNA have been cloned. The uncloned maxicircle segment contains few restriction endonuclease cleavage sites, varies in size among strains, and may be unstable in conventional cloning systems. cDNA prepared to bloodstream or procyclic trypomastigote RNA hybridized to all but one maxicircle segment, but did not hybridize to minicircles. Fourteen maxicircle transcripts were detected in RNA from both bloodstream and procyclic trypomastigotes. The coding sequences for these transcripts were localized and account for most of the maxicircle. One region of the maxicircle, which borders the variable region, was not found to be transcribed. We conclude that the maxicircle is largely but not completely transcribed in both bloodstream and procyclic trypomastigotes, whereas minicircle transcription is minimal or absent in these stages. Qualitative transcriptional differences which could account for mitochondrial respiratory differences between the bloodstream and procyclic trypomastigotes were not observed.