Pig offal will be back on sale from today after a four-month ban which followed the discovery of illegal growth stimulants in pork organ meat. The sale of pig livers, kidneys and lungs was suspended in May after the asthma drug Clenbuterol, used to make pork lean, made some meat consumers ill. Extensive testing of pigs and a tracing system was established by the Department of Agriculture and Fisheries and the Department of Health along with assistance from Urban and Regional Services departments. Four local farms were found to have used Clenbuterol, according to Agriculture and Fisheries assistant director Liu Kwei-kin. However, Dr Liu refused to comment on whether these farms had now been banned from supplying pig meat to local wholesalers. 'After a positive test, the farm is inspected and pigs tested again. We stop supply until they test free,' he said. Two farms on the mainland were found to have supplied tainted meat, but Dr Liu said that more testing would stop such cargo from entering Hong Kong in future. Four feed supply outlets in the Special Administrative Region were raided and warned, he said. Investigations into possible prosecutions were under way, he added. None of the samples taken in the past two weeks has tested positive to Clenbuterol.