Monoselenophosphate, SePO3H3-n n-, has been chemically synthesized and characterized. It has been shown to be identical with the biological selenium donor SePX. Hydrolysis of selenophosphate is pH dependent and maximal at about pH 7. The dianion is the species which hydrolyzes fastest. The hydrolysis occurs via a dissociative monomeric metaphosphate-like transition state. Alcohols and amines are phosphorylated by monoselenophosphate. The sensitivity of detection of both 77Se and 125Te by NMR spectroscopy has been greatly increased by inverse proton detection using multiple-quantum 1H-{77Se} and 1H-{125Te} correlation spectroscopy. One- and two-dimensional HMQC spectra have been obtained for a variety of organoselenium and tellurium compounds. The signal enhancement obtained by such methods are comparable to the theoretical values.