Auckland health organisations say a World Health Organisation warning about an STI which is becoming drug resistant echoes their concerns.
Gonorrhoea has broken out amongst gay and bisexual men in the city, and clinicians and lab specialists are particularly concerned that it is nearing drug resistance here.
The AIDS Foundation is among those offering increased testing services, and spokeswoman Dawn O'Connor says at the moment, it can still be treated.
"But it's a serious concern to us that A - there's an outbreak of this, and gay and bi-sexual men have this, and most of them won't know it, and B - that's it's showing signs of drug resistance.
"We're working very hard with lab tests and also with Auckland Sexual Health to try and get gay and bi-sexual men tested even if they have no symptoms at the moment, to try and stop this outbreak from spreading further."
Ms O'Connor says STIs and other diseases become much more expensive and difficult to treat when the first line of drugs starts to fail.
She says it takes time for an STI to become fully resistant and right now it can still be cured, but gay and bisexual men must get tested to get treated.