Fluoral-P or 4-amino-3-penten-2-one or acetylacetone imine (FR-0634, CAS 1118-66-7) is a member of a selective family of reagents for aldehydes. It is readily available from Frinton Laboratories, Inc. in small quantities. It is obtained as a low-melting solid mass, melting at about 38°C and boiling at 104°C at 16 mm. The stability, selectivity and reactivity of the reagent are outstanding, and has been utilized in the automatic determination of formaldehyde. It is shown that the condensation reaction between 4-amino-3-penten-2-one (Fluoral-P) and formaldehyde gives a product detectable by fluorescence. The flow injection system utilizing this reagent can be used to determine formaldehyde in the lower nanomole range. The recent findings that indoor air can contain up to 15 times the percentage of formaldehyde when compared with outdoor air has led to an increase in use of 4-amino-3-penten-2-one (Fluoral-P).