Knowing the molecular structure of a substance can help predict whether we will find its smell heavenly or malodorous, according to new research from scientists at the Weizmann Institute of Science and the University of California at Berkeley. Neurobiologist Noam Sobel of the Weizmann and colleagues suggest that their findings represent a first step in understanding the physical laws that underlie our perception of smell. The team analyzed a database of 160 different odors ranked by perfume and smell experts according to a set of 146 characteristics, including sweet, smoky, musty, etc. The team obtained a chart of pleasantness rating of the odors, ranging from sweet and floral to rancid and sickening. They could then correlate odor rank with molecular structure and predict with some flexibility whether a particular molecule will smell good or bad.