A general method to identify trace elements in biological molecules is described. These measurements are made in only a few minutes without preliminary isolation and preconcentration steps; Many unusual or difficult elements, such as Cr, Se, Cd, Th, and U, can be observed at ambient levels bound to proteins in human serum. A new protein or family of proteins, that either contain Se or that bind Se molecules, is found with molecular weight similar to 760 kDa. Binding of metal cations to DNA restriction fragments can be studied by similar procedures both for essential elements such as Mn and Fe and toxic ones such as Cd and Pb. In particular, trace Pb, Cd, and Co are completely bound to DNA fragments. Reduction of chromate to a cation (probably Cr3+) and subsequent binding of the Cr cation to DNA is also demonstrated.