The 3'termini of transcripts originating from genes organized in a highly expressed transcription unit were analyzed in the archaebacterium Methanococcus voltae. The putative termination signals were found in an AT-rich intergenic region following the 3'-terminal gene. The two detected signals both contain oligo(T) sequences. A possible stem/loop structure immediately precedes one of the oligo(T) tracts. This secondary structure is considered to have an additional function in stabilizing the transcripts.