This paper is partly statistical, partly interpretative. In general dreams are 'colourless, soundless, motionless, tasteless'; but when sensations do appear they appear in that order of frequency. The author includes an appendix on his method of scoring and assessment. These frequencies are consistent with the concept of a hierarchical structure in the organization of sensory experience, with a corresponding degree of availability in the sensory material. The reason for the absence of sensation in dreams is that sensation is loaded with affect and therefore promotes wakefulness. Sensation occurs in a dream as the harbinger of affect.