1,6-Diphenylhexatriene (DPH) is frequently used as a probe molecule in lipid bilayers to give information about membrane structure and fluidity. Besides fluorescence intensities and fluorescence decay times [5], the photoreactivity of DPH depends on the sensitivity of the excited state to the molecular environment. Quantitative measurements of photochemical quantum yields as a value for this photoreactivity are difficult to obtain, because of weak absorption and unavoidable light-scattering by the sample. Modern microprocessor-controlled apparatus can solve these analytical problems. Since commercial spectrometers even with data-output and external control-units are not programmable as automated combined irradiation and measurement devices, a self-developed apparatus was used [1]. It contains a microprocessor-controlled UV/VIS-spectrometer DMR 10, a fluorimeter Z F M 4 and DMR21 (all Carl Zeiss, Oberkochen). vesicles and micelles and for various temperatures. By use of a numerical evaluation procedure the partial photochemical quantum yields of the first photochemical reaction step can be selectively calculated without knowledge of further photoproducts [3]. It turns out, that these values drastically depend on diffusion processes, caused by different solvents and temperatin'e, especially in case of vesicular solutions. For the recording of fluorescence reaction spectra [2], an OMA-system had to be used. In conventional fluorimeters the fluorescence excitation lamp causes such a fast photoreaction of DPH during one scan cycle, that too few spectra can be taken until photodegradation for photokinetic evaluation. Besides, the information at different wawavelength belongs to different irradiation times. Intensity(I-) diagrams [2] cannot be significant. The absorbance reaction spectra [6] are recorded by the DMR 10 and stored in digitized form on data cartridges. These data can be used to calculate derivative spectra [4] and absorbance(E-)diagrams [6]. An example of a derivative reaction spectrum is given in Fig. 1. The results prove the quality of mathematical differentiation algorithms, whereas a derivation by the use of the spectrometer's internal analog device did not give the required accuracy. These derivative spectra could be used for kinetic analysis of scattering solutions were the usual kinetic analysis of absorbance values did not succeed. Microprocessor control allows the measurement of spectra at extreme conditions and the calculation of derivative spectra. These can be used to obtain reaction constants even in scattering solutions. This possibility to obtain and compare results of DPH under various conditions gives further information on the behaviour of DPH in micelles and vesicles.