The LAB Fit is a software for Windows developed for treatment and analysis of experimental data. At LABFit program you are able to: 1) Treat similar data (grouped and ungrouped dataset, two samples); 2) Treat non-similar data; 3) Determine propagated error (up to eight independent variables); 4) Plot 2D and 3D graph (normal, parametric, imported dataset, contour of maps); 5) Execute math calculations (system of linear equations, roots of function, differential equation, system of differential equations, etc); 6) Extract data (x;y) from a 2D graph (digitizing); 7) Curve Fit (almost 500 functions at the library, with 1 and 2 independent variables, functions finder, option that let you write the fit function, rejection of data, confidence and prediction bands). The LAB Fit has a menu for curve fitting and the main programs of this menu use nonlinear regression. The LABFit fits functions of one and several independent variables (from 1 up to 6), admitting uncertainties at the dependent variable (Y) and also at the independent variables (X). At the LAB Fit library there are more than 200 functions of one independent variable and almost 280 functions with two independent variables. The user disposes of a finder functions program. If necessary, there is an option so that the user can write its own fit function. Once determined the fit parameters, it