1. The pulsatile nature of luteinizing hormone (LH) secretion has recognized physiological and clinical importance, but because of the difficulties with statistical analysis of serial data the precise nature of this pulsed signal is poorly understood. Several groups have noted small-amplitude, high-frequency pulses superimposed on large slower pulses, but, using conventional methods of analysis, it is not possible to distinguish these from assay variation or to characterize them.

2. In an alternative approach we have applied the methods of time series analysis which identify the harmonic patterns within data. Twenty-four healthy women in the early follicular phase of the cycle had blood samples taken at intervals of 1, 5 or 10 min for up to 6 h.

3. We found that LH secretion consists of superimposed harmonics of varying amplitude which occur in frequency bands of about (a) 1–3 h and (b) 2–3 min. Investigations excluded a reproducible pulsatility in our LH assay, implying that the small fast pulses are physiological events.

4. We conclude that LH release is highly complex and that the methods of time series analysis permit identification and characterization of the multiple pulses.

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