In this work, ZULF NMR relaxometry was exploited to collect information about the molecular environment in chemical solutions and biofluids. The strong influence of paramagnetic oxygen on zero-field NMR spectroscopy was demonstrated by measuring spin systems with 1 H-31 P and 1 H- C couplings. In particular, we showed a strong dependence of the heteronuclear singlet-state lifetime on the concentration of dissolved oxygen. We also investigated the lifetime of N-methylpyridinium, a precursor of potential contrast agents, in the ULF regime. In particular, we demonstrated slower longitudinal relaxation of this compound in H 2 O compared to D 2 O. Nuclear magnetic relaxation dispersion profiles of aqueous solutions of a paramagnetic compound (CuSO 4 ) were studied in the ULF regime. We demonstrated that samples with and without dissolved oxygen exhibit a slightly different magnetic-field dependence, which agrees well with the relaxation theory, proving the reliability and potential applicability of the method for chemical analysis. Finally, we investigated the ULF NMR spectra of human whole blood and blood plasma. Despite the shorter (≈300 ms) relaxation times of these biofluids, the high-quality ULF NMR spectra were obtained and examined. These measurements hold promise as a new blood diagnostic technique. Without the need for sophisticated sample preparation, the blood T 2 relaxation time obtained in short measurements (< 1 min) at the ULF conditions is a potentially valuable marker of inflammation often induced by metabolic disorders, infections, etc. Our work points towards the applicability of ZULF NMR relaxometry employing atomic magnetometers as a simple, portable, robust, inexpensive, and sensitive tool in chemical and biological analysis. In addition, ULF NMR relaxometry of biofluids paves the way for molecular imaging at ZULF conditions where T 1 and T 2 relaxation properties of specific molecules predominately determine image contrast .