Uranium that is highly enriched in 235U (HEU) is also often also enriched in 234U because it too is a lower-mass isotope than 238U and thus its concentration would be preferentially increased in any mass-sensitive enrichment process. Thus the ratio 234U/238U might be regarded as a surrogate for 235U/238U—the usual measure of enrichment. For this reason it has been suggested that 234U/238U measurements be used to detect contamination by HEU. The purpose of this Note is to point out that, because of alpha-recoil effects, 234U/238U varies widely in natural systems, and for this reason it would not be a dependable indicator of the presence of HEU. The same variations would cause 234U/238U ratios to be doubtful indicators of depleted uranium.