By combining the selectivity of high-resolution laser spectroscopy with the specificity of hyperfine interactions in zero-field magnetic-resonance spectroscopy, C-13-containing isotopomers of pentacene have been observed in natural-abundance samples and H-1-containing isotopomers of penthcene in "fully" deuterated samples. Molecules containing two C-13 nuclei or up to four residual H-1 nuclei have been identified.