if( !require('drc') ){
    install.packages('drc', dependencies=TRUE, repos="http://cran.rstudio.com/")
}
library(drc)

# The example from the book:
#
RScompetition.book = nls(biomass ~ a/(1 + b*(x + c * z)), data=RScompetition, start=list(a=20, b=1, c=1))
print(confint(RScompetition.book))