Investor mortgage lending picked up in September - the second consecutive month that the market has shown signs of recovery.According to the latest Reserve Bank credit data, lenders' investor mortgage balances increased by 0.6 per cent in September, compared with the previous month.Over the 12 months to September investor mortgage balances grew by 4.8 per cent - the first increase in the annual growth rate in 18 months.The market has been subdued since the Australian Prudential Regulation Authority wrote to lenders at the end of 2014, advising them to keep a lid on mortgage lending to investors.Owner-occupier mortgage balances grew by 0.5 per cent in September, compared with the previous month, and by 7.3 per cent over the 12 months to September.Total mortgage balances grew by 0.5 per cent in September, compared with the previous month, and by 6.5 per cent over the 12 months to September.Business loan balances grew by 0.2 per cent month-on-month and by 4.7 per cent over the 12 months.Personal credit balances fell again. Balances were down 0.1 per cent month-on-month and by 1.3 per cent over the 12 months.Personal credit balances have been stuck at around A$144 billion since late 2013.