The purpose of the present research is to examine which of the two factors: (1) the iconic-semiotic factor; or (2) the human-phonetic factor is more relevant in explaining the appearance and distribution of the hand shape B-bent in Israeli Sign Language (ISL). The B-bent shape has been the subject of much attention in sign language research revolving around the question of its status as a phoneme. The arguments supporting the phonemic status of the B-bent hand shape have been primarily based on the semiotic opposition between the hand shape B and the hand shape B-bent. It has been claimed that in Italian Sign Language the hand shape B is perceptually distinct from the hand shape B-bent, i.e. in opposition to the general, neutral, unmarked meaning of the hand shape B, the iconic hand shape B-bent has a more narrow, specific and marked meaning: DELIMIT. The B-bent hand shape appears in spatial-temporal signs such as "a little before, ahead, postpone or behind". In these signs the iconic structure of the hand shape B-bent is utilized to mark borders in space and time. The arguments opposing the perceptual/phonemic distinction between these hand shapes is based on the human-phonetic factor, i.e. the need to reduce the effort on the part of the wrist joints in specific phonetic environments. We performed a quantitative and qualitative content analysis of the distribution of the basic units of 560 lexical signs taken from a stratified random sample from the ISL dictionary. The results were analyzed in the framework of the sign-oriented linguistic theory of the Columbia School including the theory of Phonology as Human Behavior. Our data revealed that the B-bent hand shape - as all the "building blocks" of the ISL--is a morpho-phonemic unit. We found that there is not only a phonemic distinction between hand shape B and hand shape B-bent in ISL (based on minimal pairs), but there is also a perceptual distinction between them. The qualitative analysis shows that the distribution of the B and the B-bent shapes in the lexicon of ISL is not random but rather motivated by a specific iconic meaning attached to each one of them. The results of our research lead to the conclusion that iconicity is the dominant explanatory factor in the Phonology of ISL. (Contains 4 figures.)