A synthetic, partially double stranded decadeoxyribonucleotide with cohesive ends, containing one potential psoralen photo‐crosslinking site centrally positioned (5′‐d(CGGGCTACCC) + 3′‐d(CCGATGGGGC)), has been ligated to double stranded DNA oligomers, which were subsequently photoreacted with 4,5′,8‐trimethylpsoralen. It was found that psoralen DNA interstrand crosslinking does not significantly alter the electrophoretic mobility of these DNA molecules in polyacrylamide gels. Based on this, we conclude that any bends in the DNA helix that may be induced by psoralen DNA interstrand crosslinking must be significantly less than the 45° proposed by Tomic et at. (1987) (Science, 238, 1722) and/or of a different nature than the DNA sequence dependent bends due to d(A)n tracts.