Four Parameter Logistic Regression

Dear All, I would like to do a four parameter logistic fitting of my data. The equation is the one at this page: http://en.wikipedia.org/wiki/EC50

However, it's not that immediate to find the EC50 and Hill slope. Is there any matlab function from some toolbox or from anyone that has implemented this kind of regression?

I found the logistic regression curve fit function in the statistical toolbox but I don't think it uses this model.

Any help or suggestion would be greatly appreciated, Thanks, Danilo