Exposure of the serosal face of anuran urinary bladder to hyperosmotic solutions (SH), results in a reversible and reproducible increase in water flux (J_w) which is similar in time course and magnitude to that elicited by AVP Bentley,1964. The hydro-osmotic response to SH and AVP in combination is additive. The SH response is absent in nominally chloride- free solutions, Hanna-Mitchell, & Gebruers, (2001), and is also inhibited by 100 μM ethylisopropylamiloride (EIPA) suggesting a role for a Na /H exchanger (NHE) in the response (Hanna-Mitchell, et al. 2003). In this study male Rana Temporaria bladders were used in a series of experiments employing a modification of the gravimetric method of Bentley (1958) to study J_w. Frogs were stunned, decerebrated, pithed and bladders were dissected out. These were filled with hypotonic Ringer, R/2, (120 mOsm.kg^-1 H₂O) and immersed in a bath of either isotonic R, 230 mOsm.kg^-1 H₂O (Control) or hypertonic R3/2, 335 mOsm.kg^-1 H₂O (SH), pH was 7.9 and temperature 19οC. Changes in J_w following immersion in SH solution was determined in the presence and absence of 1μM EIPA on either apical or basolateral faces of the bladder. This concentration is reported to inhibit more sensitive isoforms of the exchanger such as NHE₁. Flux values represent cumulative values for the 30 minute period during control or following experimental stimulation. A pilot study on the effect of 5mM BaCl₂, an agent which blocks K channels involved in cell volume regulation, was also carried out. Results were analysed using Students paired and unpaired t test as appropriate, and expressed as Mean ± S.E.M. A significant increase in flux from basal levels of 19±3 μl/30 min to 249±74 μl/30 min occurred following SH stimulation (P < 0.01, n=5). Exposure to SH in the presence of basolateral 1μM EIPA reduced Jw to 154±46 μl/30 min (P < 0.05, n=5). Exposure to SH the presence of apical EIPA reduced flux to 156±16 μl/30 min. Exposure of four bladders to basolateral 5mM BaCl₂ did not alter the SH response. In a previous series of experiments 100μM EIPA reduced flux to baseline values. The partial inhibition seen here is consistent with activation of NHE isoforms other than NHE₁ in the SH stimulated increase in water flux. The absence of inhibition in the presence of BaCl₂ would suggest that more than a simple volume regulatory response is involved in the increase in J_w. The use of specific inhibitors for NHE₁ and NHE₃ would clarify these results.