The function of HSD17B3 (hydroxysteroid 17-beta dehydrogenase 3, Ensembl gene identifier ENSG00000130948) is as follows. Catalyzes the conversion of 17-oxosteroids to 17beta- hydroxysteroids (PubMed:16216911, PubMed:23856005, PubMed:26545797, PubMed:27927697, PubMed:8075637). Favors the reduction of androstenedione to testosterone (PubMed:16216911, PubMed:23856005, PubMed:26545797, PubMed:27927697). Testosterone is the key androgen driving male development and function (PubMed:8075637). Uses NADPH while the two other EDH17B enzymes use NADH (PubMed:16216911, PubMed:26545797, PubMed:8075637). Androgens such as epiandrosterone, dehydroepiandrosterone, androsterone and androstanedione are accepted as substrates and reduced at C-17 (PubMed:16216911). Can reduce 11- ketoandrostenedione as well as 11beta-hydroxyandrostenedione at C-17 to the respective testosterone forms (PubMed:16216911, PubMed:27927697). {ECO:0000269|PubMed:16216911, ECO:0000269|PubMed:23856005, ECO:0000269|PubMed:26545797, ECO:0000269|PubMed:27927697, ECO:0000269|PubMed:8075637}.