The porosity and the mechanical strength of 64 bone cement specimens were investigated. Different types of mixing procedures were tested: 1) hand, 2) compression, 3) vacuum and 4) the combination of vacuum stirring and compression. The differences in porosity and mechanical stability are remarkable. In relation to hand-mixed bone cement all techniques are leading to a reduction in the number of cavities. Specimens made by compression are showing a confluence of several small cavities to a few large. There is only a change in the distribution of the embedded gas volume, but not a reduction. The lowest porosity is seen in vacuum mixed specimens.