Thousands protested in Urumqi over the needle attacks
No dangerous chemicals have found in blood samples from the victims of recent needle attacks in China's Xinjiang region, state media have said.
Rumours had been rife that the needles contained radioactive substances, poison or even HIV.
Blood samples from 250 reported victims were examined in a Beijing lab, said state-run Xinhua news agency.
The syringe attacks began in August, a month after riots between ethnic Uighur and Han Chinese left about 200 dead.
Three people have received jail sentences over the needle attacks.
The wave of attacks has raised tension in the region, amid long-standing animosity between the Uighur and Han communities.
A total of 531 people reported being attacked with hypodermic needles, with 171 showing "obvious syringe marks", according to Xinjiang officials.
The head of disease control at China's Academy of Military Medical Sciences said no traces of radioactive substances, toxic chemicals, HIV or other poisonous or viral substances were found in the samples they checked, Xinhua reported.
Thousands of angry residents of Urumqi, Xinjiang's capital, protested earlier this month, demanding better security over the needle attacks and swifter legal action after July's riots.
At least five people were killed in unrest around these latest protests.
The Chinese government has been struggling to restore calm in Xinjiang since the July riots, the worst ethnic unrest in the country for decades.
A number of people have been arrested and charged over the violence, but no one has been tried yet.
Three Uighurs were sentenced on Saturday to jail terms ranging from seven to 15 years for syringe stabbings or threats to use needles in robberies.