A man has been arrested on suspicion of manslaughter in connection with the death of a man suspected of using contaminated heroin.
The 41-year-old was taken ill in Great Knollys Street, Reading, Berkshire, and later died at the Royal Berkshire Hospital at the weekend.
A 36-year-old local man has been held and is in custody.
Two other men also died at the weekend which police believe could be linked to the same batch of the drug.
Post-mortem tests on these man, aged 25 and 62, proved inconclusive and further tests will be carried out.
A post-mortem examination on the 41-year-old is due to take place on Friday.
Det Insp Nick Watts said: "It remains too early for us to say whether the deaths of these men have been caused by contaminated heroin or a particularly strong batch of the drug, but it is important that drug users in the area, and the wider community, are aware of this possibility."