We report here the ability of adults to recognize the states of discomfort and comfort in babies aged three and six months by listening to their vocalizations. The acoustic characteristics of vocalizations significant for recognizing states from the characteristics of the baby’s voice are described. Discomfort vocalizations were found to differ from babies’ comfort signals in terms of the mean and maximum fundamental tone frequencies (FTF) and FTF values in the central and final parts of vocalizations. A mathematical model is presented and a function classifying signals as indicating discomfort or comfort is described. Babies’ vocalizations attributed by adults to the comfort and discomfort categories with probabilities of 0.75 and above were very reliably recognized by the mathematical model based on the classification function.