St John Ambulance is investigating claims of male paramedics sending sexually explicit images of themselves and suggestive text messages to female colleagues.
The service confirmed yesterday it was aware of one paramedic who appeared to have been "communicating inappropriately with his female colleagues".
It said it had no evidence that the sexual harassment was more widespread.
The ambulance service responded after _The West Australian _was contacted by a man who said his paramedic wife had been receiving graphic sexual images on her mobile phone from a male colleague asking her to respond if she wanted to "cuddle this".
When the woman sent a message back telling her colleague to "grow up", he sent more messages.
The messages were sent as recently as last week.
The man said his wife had discussed the text messages with other female ambulance officers who told her they had received similar messages and they appeared to be from more than one male officer.
They were mostly directed at newer and less experienced female paramedics and sent to their mobile phones.
But most were reluctant to "rock the boat" by making an official complaint, while others had responded in a "reciprocal" manner.
The man said he was particularly concerned because he and his wife had a young child who could have seen the explicit images on the phone.
The ambulance service said yesterday it was investigating and wanted any officers who had received the messages to tell their managers.
In a statement, ambulance service director Len Fiori said St John had not received any formal complaints regarding the issue but confirmed one man was under investigation.
"St John has been made aware of a male paramedic who may have been communicating inappropriately with his female colleagues," he said.
"This sort of behaviour is unacceptable to the organisation and it will not be tolerated."
St John would not say if the paramedic who sent the messages was still working or facing disciplinary action. The service employs about 600 ambulance officers and paramedics.
The paramedics' union, United Voice, did not respond to calls.