Mainlanders are facing steep bills for DNA tests to prove they have the right of abode in Hong Kong. Zhongshan Medical University says it is the only authorised testing agent in Guangdong. The institute charges $790 (850 yuan) for mainland residents and $1,218 for residents of Hong Kong and elsewhere. True parentage can only be confirmed with test results of both parents and child. More than 20 families have contacted the institute since Friday's High Court ruling. Its DNA tests are recognised internationally when assessing immigrants for family reunions. Beijing and SAR immigration authorities said after two days of talks on Tuesday they would join forces to estimate the huge number of illegitimate children stranded on the mainland. Director of Immigration Ambrose Lee Siu-kwong said one of the methods to establish eligibility would be DNA testing. But he did not say who would conduct the tests. A director of the DNA testing division at the Guangdong institute said people seeking the tests had to provide a reason. 'We have been authorised by the Guangdong Public Security Bureau to conduct tests for those families not bound by wedlock,' he said. But he had no idea if residents of Shenzhen and in other provinces would also have to travel to the Guangzhou testing centre for certificates. Guangzhou's Public Security Bureau could not confirm the authorisation yesterday, saying it would make an announcement soon. A spokesman said no applications for one-way permits would be processed for illegitimate children and those born before their parents became Hong Kong permanent residents until further instructions were received from Beijing.