Last "+theme_bw()" to be deleted. Try this: ggplot(data1, aes(x=x1, y=y1))+ geom_point()+ geom_smooth(method="glm", family="gaussian",aes(linetype="equation1"))+ geom_smooth(aes(x=x1, y=y1, linetype="equation2"),data=data2, method="glm", family="gaussian")+ scale_linetype_manual(values = c("solid","dashed"),name="Equations", labels = c("Equation 1","Equation 2"),guide="legend")+ theme(plot.title = element_text(lineheight=.8, face="bold"), legend.position="top") -- GG http://around-r.blogspot.it [[alternative HTML version deleted]]