The use of [alpha-33P]deoxyadenosine 5'-triphosphate ([alpha-33P]dATP) in DNA sequencing has been described. 33P has a maximum beta-emission energy that is 50% stronger than 35S, but fivefold weaker than 32P. As a result, sequences generated using [alpha-33P]dATP have short exposure times like 32P, yet they maintain band resolution similar to 35S. Handling of [alpha-33P]dATP is straightforward because no special lead or Plexiglas shielding is necessary.