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A new portable photoacoustic and fluorescence photometer has been built. The instrument is especially made for field measurements but can also be used indoors. This new instrument has many advantages. It can measure the photosynthetic O2 evolution and energy storage, and the vitality index in the same sample. The system is very compact, which makes it easy to transport. A small electrical generator satisfies the 110 V power requirement for field applications. All manipulations are computer controlled including the data acquisition and treatment. The photoacoustic signal‐to‐noise ratio for carbon black is the same under field conditions as in the laboratory (∼2×104) at 130 Hz. Results obtained on declining sugar maple trees in the field are presented. The combination of photoacoustic and fluorescence measurements in one instrument represents a very powerful tool in photosynthesis research.