Instrumentation and major processing components comprising a combined ultrasound and photoacoustic imaging system. Photoacoustic signal, generated by the optical absorption of laser energy by the sample, is received by an ultrasound transducer, beamformed and processed to form an photoacoustic image. Ultrasound, appropriately beamformed, is emitted by the transducer, and reflected ultrasound is received, beamformed and processed to form the ultrasound image.