SummaryCompared to more consuming methods of assisted fertilisation (IVF/ICSI), insemination treatment is the easiest procedure in reproductive medicine. Due to low costs and natural treatment insemination is often the first treatment option facing childlessness although success rates are low (5- 15%). Furthermore the outcome depends heavily on the women?s age and the quality of the sperm. This study shows that the addition of theophylline during a density gradient centrifugation significantly improves sperm mobility. 100 ejaculates with particular inclusion criteria were screened. Native ejaculate was splitted and motility (WHO, 1999) sperm concentration were analysed with and without use of theophylline. Thereafter, a density gradient centrifugation with both samples (with and without theophylline) was performed and both parameter (motility, concentration) were re-analyzed. Percentage of motility A sperm is doubled by theophylline in both the native and processed ejaculate. On the contrary sperm with motility grade B were slightly reduced in the samples (native, processed) without addition of theophylline. The distribution of the percentage of the motility grades in the native ejaculate with/without theophylline and in the gradient centrifugation with/without theophylline showed a continuous rise of 50% for all four ejaculate conditions. The percentage of B-sperm sank from 63% to 30%. Reasons are the centrifugation method and the effect of theophylline. In order to prove the effect of theophylline statistically I performed a Chi-square test. Both in the native ejaculate and after the gradient centrifugation there was a significant difference between the motility grades with theophylline and the ones without theophylline (p<0.001). It could thus be shown that theophylline does not only activate immotile sperm but it also makes already motile sperm more active, which is beneficial for an IUI.