Lincolnshire police say officers were called to Norfolk Street in Boston at 9.25pm on Friday 8 May after a report that a 57-year-old man had fallen and hit his head.
On arrival, officers found that the man had died.
A 50-year-old woman and a 45-year-old man were arrested and are in custody.
In a statement headlined two arrested on suspicion of murder, a spokesperson for Lincolnshire Police said Investigating officers are keeping an open mind over what happened.
They said: "If you have information which could help our investigation, please make a report in one of the following ways:
• By calling 101 quoting the reference 485 of 8 May
• By emailing [email protected] - please remember to put the reference 485 of 8 May in the subject box
• You can also contact us through the independent charity Crimestoppers, anonymously, on 0800 555 111 or online at crimestoppers-uk.org