There is considerable interest in the symbiotic bacteria that at least some glossiphoniids house in specialized organs called bacteriomes.

Haementeria as well as Placobdelloides have Enterobacteriaceae symbionts, while Placobdella harbours peculiar and independently derived alphaproteobacteria.

As with all blood- or haemolymph-feeding leeches, their saliva, contains anticoagulant compounds which are potentially useful in therapy of some cardiovascular diseases.

Antistasin and related inhibitors of thrombokinase a such as ghilanten, lefaxin and therostatin have been derived from Haementeria species and Theromyzon tessulatum.

Ornatins, which are antiplatelet glycoprotein IIb-IIIa antagonists, were discovered in Placobdella ornata, and several species have yielded hyaluronidases.