This paper presents the results of genetic testing in two cases of shared paternity between half-siblings. In the first example, the research was based on the analysis of half-siblings and their mothers with respect to 21 autosomal markers. In the second, the research was based on both the analysis of 30 autosomal markers and X chromosome markers in putative sisters and the mother of one of them. Selected examples are presented to illustrate how the use of different research strategies affects the outcome of the likelihood ratio and the ability to make inferences in complex kinship cases.