A correlation for predicting the extent of electrohydrodynamic enhancement of natural convection from heated horizontal cylinders is presented. This correlation is supported with results from two different experiments; the first involves natural convection from a thin platinum wire immersed in R-123 with a uniform electric field, while the second involves natural convection from a flooded tube immersed in R-123 in a non-uniform electric field. The Nusselt number enhancement is correlated in terms of a "corrected electrical Rayleigh number", Ra-El, to account for the effect of a non-uniform electric field on natural convection. The correlation is valid for the range 4.0 x 10(3) less than or equal to Ra-El less than or equal to 8.0 x 10(8). (C) 2000 Elsevier Science Ltd. All rights reserved.