We conducted a retrospective statistical analysis of the Heyman, Saltzman, Whalen 1966 study of 22 stroke patients treated with hyperbaric oxygen (HBO2)--13 of them one to five hours post-stroke. We examined patients who received HBO2 treatment within seven hours post-stroke. An exploratory logistic regression analysis examining the influence of time post-stroke, time in chamber and dose of HBO2, range 2.02 atmospheres absolute (ATA) to 3.04 ATA, was conducted. Only time post-stroke was a significant influence for recovery, with each passing hour decreasing the chance of at least partial transient recovery by 62% - odds ratio: 0.38 (95% CI: 0.15 -0.95), p = 0.039. In the one- to five-hour group of 13 patients, nine (41% of 22) had recovery or recovery with relapse. This represented 69% (+/- 25% SE) of this time frame. Only two of the nine had permanent recovery. Past six hours poststroke, only one patient (11% +/- 21% SE) had partial recovery with relapse. The other eight past six hours had no recovery at all. The first three hours post-stroke HBO2 administration has the most promise for efficacy and improvement of rtPA therapy. HBO2 may also prove to be a useful challenge pre-rtPA administration to assess the risk-benefit ratio for giving rtPA.