A man walked into a staff office at Preston train station and defecated on the floor, say police.
The incident is said to have happened in an office on platform one at around 11.11pm on Saturday March 17.
Police say they are analysing CCTV as part of their investigation.
A spokesman for British Transport Police said: "We were to reports that a man defecated on the staff office at Preston station.
"An investigation is now underway."
Enquiries are ongoing.
Anyone with information is asked to contact BTP by sending a text to 61016 or by calling 0800 40 50 40 quoting reference 686 of 17/03/2018..