Small biotech Global Blood Therapeutics ( GBT) soared in heavy trading on the stock market Friday after its drug for sickle-cell disease succeeded in an early-stage trial, sending potential competitor Bluebird Bio ( BLUE) sharply downward.

At the annual European Hematology Association (EHA) meeting in Copenhagen, Global Blood gave a 90-day update on an ongoing trial of its drug GBT440, which increases the oxygen affinity of hemoglobin, thereby decreasing the sickling of the cells that brings severe anemia. The company reported a median 70% reduction in sickled cells among the patients, along with higher levels of hemoglobin and lower rates of hemolysis, or red-blood-cell destruction. There were no serious adverse events.

“We are highly encouraged by not just the magnitude of the median hemoglobin increase … but also the consistency of hemolysis marker improvement and excellent safety,” wrote Cowen analyst Ritu Baral in a research note. “While datasets released at EHA were not without some quirks, likely due to small patient numbers, overall data exceeded our high expectations.”

Global Blood stock was up about 21% in early afternoon trading to a five-month high on the stock market today, near 27.

Sickle-cell disease is a dangerous condition and is currently without a treatment, so Global Blood received the FDA’s orphan-drug designation late last year, granting seven years of market exclusivity if GBT440 makes it through subsequent trials. But it’s in a race with Bluebird Bio, which is working on a gene therapy for the disease.

Bluebird’s therapy showed such strong results with a single patient that observers were wondering if it might have even found a cure. Subsequent data with more patients produced more ambiguous results, however, though the numbers are still very small.

Bluebird stock was down about 8% intraday, near 42.