diff --git a/R/planMod.R b/R/planMod.R
index 9678047..642a528 100644
--- a/R/planMod.R
+++ b/R/planMod.R
@@ -68,7 +68,10 @@
 #'   fitMod.
 #' @author Bjoern Bornkamp
 #' @seealso [fitMod()]
-#' @references TBD
+#' @references Pinheiro, J.C. and Bornkamp, B. (2017). Designing phase II dose-finding studies: sample size, 
+#' doses, and dose allocation weights.  Handbook of Methods for Designing, Monitoring, and Analyzing Dose-Finding 
+#' Trials, Chapter 13, Chapman and Hall/CRC, 229-246.
+#'
 #' @examples
 #'
 #' \dontrun{