A3, A03, A-3, A.3, A.III or A 3 can refer to: In business: A3 paper, a paper size defined by ISO 216 In biology: A3 regulatory sequence for the insulin gene Adenosine A3 receptor, a human gene Annexin A3, a human gene Brachydactyly type A3, a disease Urea transporter A3, a trans-membrane protein HLA-A3, a Human MHC Serotype HLA-A British NVC community A3 (Spirodela polyrhiza - Hydrocharis morsus-ranae community), a British Isles plants community Subfamily A3, a Rhodopsin-like receptors… (More on A3)