In this work I analysed the outcome of growth hormone replacement treatment in patients with inherited form of multiple pituitary hormone deficiency and examined diseased-causing mutations of pituitary transcription factor genes which may underlie this disorder. The results showed that after treatment for a longer than 7-year period with a growth hormone preparation available under well-controlled distribution, the mean height of children with growth hormone deficiency reached the normal national reference range adjusted for age and sex. After establishment of clinical criteria for screening PROP1 gene mutations, I performed mutational analysis of all coding exons of this gene in 35 patients with inherited form of multiple pituitary hormone deficiency. With these studies, diseases-causing PROP1 gene mutations were detected in 15 of the 35 patients (43%). It was also found that more than 80% of mutant alleles were accounted for by those containing the 150delA and 301-302delGA mutations of the PROP1 gene. Importantly, these findings indicated a high relevance of mutational "hot spots" of the PROP1 gene in Hungarian patients with inherited form of multiple pituitary hormone deficiency and they also offered an opportunity for the development of rational and cost-effective screening strategy. When clinical and hormonal findings of patients with and without PROP1 gene mutations were compared, results showed that growth hormone deficiency was diagnosed at earlier age of life in patients with PROP1 gene mutations, but the severity of growth retardation at the time of diagnosis of growth hormone deficiency or the age of patients at the time of manifestation of other pituitary hormone deficiencies (TSH, LH, FSH and ACTH) were similar in the two groups of patients. In 15 patients inherited form of multiple pituitary hormone deficiency who had no PROP1 gene mutations, exon 6 of the POU1F1 gene containing a mutational "hot spot" was also examined but no mutations were found. Thus, these results do not support a significant role of the mutational "hot spot" of the POU1F1 gene in Hungarian patients with inherited form of multiple pituitary hormone deficiency. Finally, I introduced a method for the detection of mutations of the PITX2 gene, a pituitary transcription factor that plays a role not only in pituitary development and differentiation but also in the lateralization of organs. With the use of this method, I performed mutational analysis of all coding exons of this gene in an exceptionally unique patient who had both situs inversus totalis and inherited form of multiple pituitary hormone deficiency, but no mutation was found. Thus, the findings in this patient failed to indicate that mutation of the PITX2 gene is involved in the pathomechanism of situs inversus totalis associated with inherited form of multiple pituitary hormone deficiency.