hi! i fixed a bug in the function read.affy (which is called by the subset method "["). FYI, the problem arose because class(data.frame(x=1:10,y=1:10)[,1]) is NULL. i assumed it would be data.frame. as a consequence i was creating a phenoData object with a non data.frame object in the pData slot. to fix it i just did: data.frame(class(data.frame(x=1:10,y=1:10)[,1]) ) i hope this doesn't offend the real programmers. Rafael