Abstract This study utilized normal and defective epithelial cell cultures and epidermal skin samples to examine intra- and intercellular calcium signaling. The main interests of this thesis were Hailey-Hailey disease (HHD), Darier disease (DD), neurofibromatosis 1 (NF1) and transitional cell carcinoma (TCC). HHD and DD diseases are rare autosomal dominant skin disorders characterized by dissociation of epidermal keratinocytes (acantholysis) at the suprabasal layer of the epidermis. HHD and DD diseases are caused by mutations in the genes encoding the calcium pumps in the Golgi apparatus (hSPCA1) and endoplasmic reticulum (SERCA2b), respectively. Due to these mutations calcium uptake into the Golgi apparatus or ER is diminished, which is believed to cause abnormal cell junction protein processing and dissociation of keratinocytes. This study utilized electron probe microanalysis (EPMA) and demonstrated for the first time that lesional areas of HHD and DD and non-lesional areas of DD epidermis display abnormally low calcium content in the basal cell layer. Furthermore, ATP mediated calcium signaling was impaired in cultured HHD and DD keratinocytes and epidermal ATP receptor localization was disrupted. In conclusion, these results suggest that the low calcium content in the basal cell layer is the reason for suprabasal ruptures in HHD but not necessarily in DD lesions, and that abnormal ATP receptor localization contributes to the calcium signaling defects. NF1 deficient keratinocytes display abnormally low resting cytosolic calcium levels and it has been suggested that the calcium concentration in the lumen of the endoplasmic reticulum is decreased. This study demonstrated that NF1 keratinocytes rely mostly on ATP mediated calcium signaling while normal keratinocytes rely mostly on gap junctional intercellular communication (GJIC). Studies with TCC cells have demonstrated that gap junctions participate in intercellular calcium wave propagation. This thesis demonstrated that the ATP mediated pathway was also operational in calcium wave propagation in normal uroepithelial and TCC cell cultures. Furthermore, impaired calcium wave propagation in the TCC cell culture could be improved through PKC α/βI –isoenzyme inhibition with Gö6976. Gö6976 treatment increased connexin 26 clustering at plasma membrane but did not alter expression level of the protein. This thesis contains a wide repertoire of calcium detection techniques including a new cutting-edge technology for elemental calcium detection of epidermal samples. These techniques can be used for molecular specific analysis of calcium signaling in epithelial cells.