An analyzer for chemical assays includes a turntable which supports sample containers and reagent containers within a cooled volume and test cells about the periphery of the cooled volume. A probe is carried by a rotating arm for withdrawing liquid from the containers and dispensing the liquid. Fixed stations are also provided in the path of the probe. One such station serves to both wash the tip of the probe and to receive samples for flow-through analysis. Heaters associated with the probe and with the test cells increase the rate of reaction. Curved walls of test cell segments match the optics of an optical analyzer so that light from the analyzer lamp is generally orthogonal to the curved surfaces. The light voltage of the lamp may be controlled as a function of lamp wavelength required for particular assays. The system provides multiple-point calibration and automatic dilution of samples. Multiple aliquots of reagent may be drawn into the probe and then be dispensed into separate test cells. Individual aliquots of sample may be drawn and dispensed with the reagent.