Single dish studies of molecular abundances in the envelopes around a large sample of 18 low-mass pre and protostellar objects were presented. Typical grain mantle products and organic molecules, including H₂CO, CH ₃OH, and CH₃CN were studied. It was found that with a few exceptions, all H₂CO lines can be fit by constant abundances of 7x10^-11-8x10^-9 throughout the envelopes if ortho and para lines are considered independently. An improved fit to the data was obtained with a 'drop' abundance structure in which the abundance is typically few x 10^-10 when the temperature is lower than the evaporation temperature.