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The larvae of Pelobates syriacus have a long developmental period to metamorphosis. This is atypical of xeric- inhabiting anurans and suggests that the populations of this species in Israel are relicts from the time when this region enjoyed a milder climate. In contrast, metamorphic climax is rapid. In the course of a few days the external appearance changes from that of tadpole to toadlet. During the same short period, together with other internal reorganizations, the kidney completes its maturation from pronephros to mesonephros. The production of urine, a fluid which is almost identical to plasma in the tadpoles, ceases, and when it is resumed in postmetamorphic toadlets, it is dilute and adult-type with nitrogen as urea replacing ammonia. There is a simultaneous increase in plasma osmolality. In P. syriacus a long period of development followed by the emergence of a relatively large metamorph may be an adaptation to a hostile environment. Coupled with the rapid metamorphic climax, these life history features may increase the opportunities to disperse and burrow into soil that remains moist, at the beginning of a long hot and dry summer.