We have investigated Adenovirus-2 promoter function with attention to: 1) the activity of the major late promoter at early times, and 2) the fine structure of Ad-2 mRNA 5' termini, and the relationship of these structures to the DNA sequences which encode them. A) RNA hybridizing to DNA from coordinates 16-59 accumulates in the nucleus at a rate comparable to the accumulation rate of classical early transcription unit RNA. B) Polyadenylated RNA from Bam 1 D (late 3-coterminal family L1) and to a lesser extent Bam 1 C (families L2 and L3) accumulates in the cytoplasm. C) Early nuclear RNA selected by coordinate 15-17 DNA gives a RNAse T-1 fingerprint pattern qualitatively identical to that obtained with late nuclear RNA, and includes the capped undecanucleotide and promoter proximal spots 1-4 (Ziff & Evans, 1978). These results demonstrate that the coordinate 16.4 promoter functions in mRNA synthesis at early times. D) 5' ends map downstream from an AT-rich region ("Hogness Box", positions -31 to -25). E) The heterogeneous 5' termini arise from a 2-6 base region with a fixed position relative to the Hogness Box. F) Within this region, purine termini are greatly favored over pyrimidines.