Abstract: The invention relates to a transmitted-light refractometer wherein a slit diaphragm is imaged on a diode array through a cuvette holding the sample. The cuvette itself is arranged in the telecentric beam path. The exit window of the cuvette has several regions in which the inner surfaces of the exit window are inclined differently to the inner surface of the entry window. In this way, several slit images are generated on the diode array and the relative spacings of these images are independent of a possible disadjustment of the condenser and the objective. An embodiment of the invention permits the simultaneous measurement of the refractive index and the absorption of the sample.