Abstract An in vitro perifusion system employing very frequent (30 s) perifusate collectionswas utilized to investigate the relationship between pulsatile release of luteinizing hormone (LH) and immunoreactive beta-endorphin (ibeta-END) during individual perifusions of adult human anterior hemipituitaries. Each of six hemipituitaries released LH and ibeta-END in a distinctlypulsatile fashion, with pulses occurring approximately every 3.2 min for each. Power spectral analysis revealed that pulsatile release of both LH and ibeta-END occurred in a rhythmic pattern, with a periodicity of 3.1 and 3.2 min, respectively, and that the periodicity of pulsatile LH and ibeta-END release was correlated within individual perifusions. Moreover, the relative amplitudes (% change) of the synchronous LH and ibeta-END pulses were correlated. The effluent fractions from two of the perifusions were also assessed for thyrotropin, and it was determinedthat thyrotropin pulses were synchronized to both LH and ibeta-END pulses. These studies confirm that LH and ibeta-END are released from human anterior pituitaries in vitro in an intrinsically pulsatile fashion, and demonstrate that the LH and ibeta-END pulses tend to occur rhythmically and in synchrony and proportion with each other. Furthermore, correlation of thyrotropin pulses to both the LH and ibeta-END pulses suggests a common fundamental intrapituitary pulse generating mechanism.