The information that I was able to find indicate that it would require sending tissue samples to a well-equipped botany lab, for chromosome counts, or a plant genetics lab for identification of sex alleles. If you think it worth the trouble, you might want to check with a university, since they may want to make it an excercise for their advanced agriculture or botany students.

thanks for info, i'm not a commercial grower, only growing for fun and family, seems' too complicated for a few plants, cheers, alun

A lot of hooraw for a backyard grove, it's true! :)
Since papayas can be short-lived, you might want to remove some of the males as soon as you know what they are, and replace them with new seedlings. That way you have 25% males, instead of 50%. Sometimes you get lucky, and get a tree with both male and female flowers.

thanks, good idea, didn't know had male/female trees, cheers