A relation is obtained between the total pi-electron energy E-pi and the HOMO energy E-HOMO, valid within the HMO approximation. This seems to be the very first relation between E-pi and E-HOMO ever established. It enables a much more accurate assessment of E-pi of alternant conjugated hydrocarbons than that based on McClelland's formula and on other (n, m)-type approximate expressions. (C) 2016 Elsevier B.V. All rights reserved.