Abstract
We investigate how the dynamics of a mathematical model of a nephron depend on the precise form of the delay in the tubuloglomerular feed- back loop. Although qualitative behavioral similarities emerge for di®erent orders of delay, we ¯nd that signi¯cant quantitative di®erences occur. With- out more knowledge of the form of the delay, this places restrictions on how reasonable it is to expect close quantitative agreement between the mathemat- ical model and experimental data.