Fluorotelomer unsaturated aldehydes and acids (FTUALs and FTUCAs) are intermediate metabolites that form from the biotransformation of fluorotelomer-based chemicals. FTUALs and FTUCAs have been previously suggested to contribute to the toxicity associated with human exposure to fluorotelomer compounds by covalently binding to biological nucleophiles. However, the extent of their reactivity has only been assessed with glutathione. The purpose of the present study was to assess the reactivity of these intermediate metabolites with a series of nucleophilic amino acids and model proteins. In vitro experiments were carried out in an aqueous buffer system to determine the reactivity of nucleophilic amino acids with FTUCAs and FTUALs having varying fluorinated chain lengths. Using (19)F NMR spectroscopy to monitor the disappearance of the FTUCAs and FTUAL signals and the production of a fluoride signal, reaction rate constants were determined under pseudo-first-order conditions. The FTUCAs reacted only with cysteine with the following second order rate constants: 3.63 (± 1.37) × 10(-5) min(-1) mM(-1) (4:2 FTUCA), 1.19 (± 0.91) × 10(-5) min(-1) mM(-1) (6:2 FTUCA), and 4.56 (± 0.94) × 10(-5) min(-1) mM(-1) (8:2 FTUCA). The FTUALs were significantly more reactive than any of the FTUCAs with reactivity decreasing in the following order: cysteine >> histidine > lysine >> arginine. The following second-order rate constants were obtained: 5.7 (± 4.2) × 10(-4) min(-1) mM(-1) (histidine), 4.3 (± 1.4) × 10(-4) min(-1) mM(-1) (lysine), and 1.4 (± 0.73) × 10(-4) min(-1) mM(-1) (arginine). FTUCAs and FTUALs were also reacted with model proteins to assess their potential for forming covalent adducts. Electrospray ionization mass spectrometry (ESI-MS) was used to investigate the stoichiometry of FTUCAs and FTUALs covalently bound to apomyoglobin (ApoMg) and human serum albumin (HSA). FTUCAs were not reactive, whereas two measurable FTUAL adducts were formed with both ApoMg and HSA at each of the FTUAL chain lengths (6:2, 8:2, and 10:2). This is the first study to probe the reactivity of FTUALs and FTUCAs with nucleophiles other than glutathione, further elucidating possible FTUAL and FTUCA fate within biological systems.