The candidate piscicide, 2-(digeranylamino)-ethanol, (commonly known as GD-174) was subjected to efficacy trials in ponds under a wide variety of conditions. Results of the trials were disappointing considering that laboratory tests had shown the compound to be selectively toxic to common carp (Cyprinus carpio). Results of pretreatment, on-site toxicity tests were misleading and indicated concentrations that failed to kill all of the carp in 19 of 23 ponds. In a few instances, the chemical killed the carp with little or no effect on nontarget fishes. No fish were killed in some trials and large numbers of nontarget fishes were killed in others. Twenty of 25 pond trials were judged to be unsuccessful. Success or failure of pond treatments could not be correlated with any particular combination of physical, chemical, and biological factors. Because the activity of GD-174 against mixed populations of fish cannot be predicted, further development of this compound as a selective toxicant for carp has been discontinued at the National Fishery Research Laboratory.