machines tend to be behemoths, taking up entire rooms in chemistry laboratories. Shrinking the machines has proved difficult, however, because of the extremely uniform magnetic field that the technique requires. In the current issue of the journal Science, an international team of researchers reports on a mobile NMR sensor that uses bursts of radio frequencies to compensate for irregularities in the small machine's magnetic field. The portable scanner (shown here testing a car tire) has part-per-million resolution and collected a spectrum in only three minutes, suggesting that moveable NMR machines may soon be routinely examining objects in their natural environments.