Hi there, If the textbox validated by the second custom validator is empty, then the client side function address1 never gets called as it is considered true by default. For more information, you can see CustomValidator Class[^] So in this case, you can use RequiredField Validator instead, however, you are required to provide some script to enable/disable the RequiredField validator depending on the status of the radio buttons as you may not want it to run when the first radio button is selected. Another idea is to develop your own custom validator which accepts an empty textbox to validate. For more information, you can see Developing a Validator Control[^] Just some ideas.