Time series analysis (TSA) is a technique to describe the structure and forecast values of a particular variable based on a series of sequential observations. This paper shows the feasibility and complementary use of TSA with a case study of metaphor use in psychotherapy sessions. A conceptual sketch of how TSA components (trends, seasons, cycles and irregular fluctuations) relate to discourse components is followed by a step-by-step assay of two therapist–client dyads.