there are some photos missing from my iphoto library. they seem to be out of sight but still there.

You looked at every photo?

Did you try to Export from the File menu? Just select the Album or Event then go to File-->Export to specify a location.

Care to share which OS you are using? Which iPhoto version?

Have you tried restarting your MBP? Repairing permissions?

What is the format of the external USB hard drive?

If it's not OS X Extended (journaled) with ownership set to be ignored you'll need to copy the library to another drive and reformat the drive that it's on now.

OT

Then try the following: apply the two fixes below in order as needed:

Fix #1

Launch iPhoto with the Command+Option keys held down and rebuild the library.

Since only one option can be run at a time start

with Option #4 and then #1 as needed.

Fix #2

Using iPhoto Library Manager to Rebuild Your iPhoto Library

1 - download iPhoto Library Manager and launch.

2 - click on the Add Library button, navigate to your Home/Pictures folder and select your iPhoto Library folder.

3 - Now that the library is listed in the left hand pane of iPLM, click on your library and go to the File ➙ Rebuild Library menu option.

4 - In the next window name the new library and select the location you want it to be placed.

5 - Click on the Create button.

Note: This creates a new library based on the LIbraryData.xml file in the library and will recover Events, Albums, keywords, titles and comments. However, books, calendars, cards and slideshows will be lost. The original library will be left untouched for further attempts at fixing the problem or in case the rebuilt library is not satisfactory.