A Fourier transform infrared (FTIR) spectroscopic method was developed to quantify ammonia (NH₃) and carbon dioxide (CO₂) to facilitate accurate determination of antennal sensitivity of adult Caribbean fruit flies, Anastrepha suspensa (Loew), to these compounds. Electroantennogram (EAG) recordings were made from antennae of flies that were exposed to known quantities of each of the pure gases and to mixtures of these gases. EAG response to volumetric dilutions of saturated vapor from a commercially available ammonium bicarbonate lure was determined, and FTIR analysis was used to measure the amount of NH₃ and CO₂ in the samples. Maximal EAG responses were elicited with doses ≥24 μg NH₃ and ≥57 μg CO₂. Mean female response was greater than male response to substrates that included CO₂. For both sexes, EAG response to NH₃ was greater than response to CO₂. When NH₃ and CO₂ were combined either as a mixture of pure gases or as vapor emitted from the lure, the EAG response was approximately equal to the sum of the individual responses to the two compounds. A polynomial regression was the best fit for describing antennal response to ammonia, carbon dioxide, and mixtures of these chemicals whether obtained from pure gas sources or from commercial lures.