The use of trace elements to mark insects internally has been studied with several insect species. It would be valuable to have access to marked parasites and predators when studying their efficacy, movement, and dispersal, thus distinguishing released parasites and predators from others indigenous to the release area. We selected for study the element rubidium (Rb) as an internal marker for two important natural enemies of Heliothis spp. on cotton, the egg parasite Trichogramma pretiosum Riley, and the predator Chrysoperla rufilabris Burmeister. Eggs of Sitotroga cerealella (Olivier) are used as the host in many mass rearing programs of Trichogramma spp. We were able to obtain an internal Rb mark in T. pretiosum by rearing them on Rb-marked S. cerealella eggs obtained from adults reared on wheat previously soaked in an aqueous solution of RbCl. Wheat soaked in water containing 4, 8, 16, and 32 mg RbCl per 100 ml water absorbed 0.265, 0.448. 0.923 and 1.4 ppm Rb, respectively. Sitotroga eggs from adults reared on the treated wheat contained 0.0023, 0.0033, 0.0052 and 0.0081 Rb per egg, respectively, while Trichogramma adults emerging from treated Sitatroga eggs contained 0.0008, 0.0013, 0.0022, and 0.0042 µg Rb/adult, respectively. A total of 93.3%, 96.7%, 97.4% and 100.0% of the T. pretiosum adults emerging from Sitotroga eggs from the 4, 8, 16, and 32 µg RbCl treated wheat, were marked, respectively. Chrysoperla rufilabris adults were fed a paste diet consisting of Wheast^®, sucrose and water, but containing 1% or 2% RbCl by dry weight. Eggs obtained from adults feeding on the diet with 1.0% RbCl contained 0.0808 pg Rb per egg with 98.7% of the eggs containing a detectable mark, and those from diets with 2% RbCl had 0.1215 µg Rb/egg, with 99.4% having a detectable mark. Larvae obtained from these eggs had 0.0103 pg/larva and 0.0184 pg/larva from the 1% and 2% diets, respectively, while adults had 0.0063 pg/adult and 0.0102 pg/adult, respectively. Results from these studies indicate that both T. pretiosum and C. rufilabris can be effectively marked with Rb.