 They found that hydroxyurea treatment could increase recipients' blood levels of hemoglobin F, a form of hemoglobin primarily made by the fetus (and normally only at low levels in adults) that is not affected by the sickle cell mutation.The results were encouraging, so in the 1990s he and a colleague, pediatrician George Dover, who had been researching sickle cell disease for 20 years, launched a controlled clinical trial.The result was such a dramatic improvement in the condition of the test group that the trial was halted early, so that the control subjects (those receiving a placebo) could benefit from the treatment.