Police believe the men, who were in their 30s, had been using heroin.
One man was discovered in the garden of a house in Stockwell, south-west London, and another was found in a car park in Kennington, south-east London.
Det Insp Keith Richardson said the batch could pose an "immediate and lethal threat" to drug users.
'Immediate' threat
Officers were called after a body was found in the front garden of a house in St Michael's Road at 0800 GMT on Tuesday.
Shortly after 2100 GMT the same day the body of a man was found in an underground car park in Lollard Street.
Both men were found with syringes and other drugs paraphernalia close by.
Mr Richardson, said: "We are warning drugs users in Lambeth and the surrounding area to be especially careful.
"Drugs are always dangerous, but we are concerned that a particular batch currently in circulation may pose an immediate, lethal threat."
Police are still awaiting the results of post-mortem tests.
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