There are disclosed novel compounds which are derived from 22,23-dihydro avermectin Bla aglycone, 13-deoxy-22,23 dihydro overmectin Bla aglycone and 13-deoxy-22,23-dihydro overmectin Blb aglycone. The six compounds are hydroxy adducts of the substrate avermectin compound at the 12a, 24, 24a, 26, 26a and 27 positions. The hydroxy adducts are prepared by incubating the substrate with the microorganism Cunninghamella blakesleeana and isolating the hydroxy adducts from the fermentation broth. The compounds are highly potent antiparasitic, insecticidal and anthelmintic agents.