Abstract: Apparatus for carrying out in situ chemical analysis of biological fluids is disclosed. A test package adapted for use with spinning rotor includes a sample-compartment, an integral cuvette and compartments for prepackaged reagents. The latter are adapted to be introduced via breakable seals into the sample compartment which contains the sample to be analyzed. The sample and reagents are then introduced via another breakable seal into a cuvette. Under pneumatic and rotational forces, mixing and measuring are carried out in situ. The rotor includes a programmable pressure applying arrangement whereby the dispensing of reagents and the movement of the latter and sample into a cuvette are controlled. Optical measurements are then carried out in situ.